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JET Manual 38WPS-Basic

Laboratory Training and Fluid QA/QC

Version 1.0

JET Manual 38 WPS-Basic Laboratory Training and Fluid QA/QCInTouch Content ID# 4298920 Version: 1.0 Release Date: June 05, 2007 Owner: Well Services Training & Development, IPC

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Copyright © 2007 Schlumberger, Unpublished work. All rights reserved.This work contains the confidential and proprietary trade secrets of Schlumberger and may not be copied or stored in an information retrieval system, transferred, used, distributed, translated or retransmitted in any form or by any means, electronic or mechanical, in whole or in part, without the express written permission of the copyright owner.

Trademarks & service marks“Schlumberger,” the Schlumberger logotype, and other words or symbols used to identify the products and services described herein are either trademarks, trade names, or service marks of Schlumberger and its licensors, or are the property of their respective owners. These marks may not be copied, imitated or used, in whole or in part, without the express prior written permission of Schlumberger. In addition, covers, page headers, custom graphics, icons, and other design elements may be service marks, trademarks, and/or trade dress of Schlumberger, and may not be copied, imitated, or used, in whole or in part, without the express prior written permission of Schlumberger. A complete list of Schlumberger marks may be viewed at the Schlumberger Oilfield Services Marks page: http://www.hub.slb.com/index.cfm?id=id32083

An asterisk (*) is used throughout this document to designate a mark of Schlumberger.

Other company, product, and service names are the properties of their respective owners.

iiiJET 38 - WPS-Basic Laboratory Training and Fluid QA/QC |

TableofContents

1.0 Introduction 51.1 Learning objectives 5

2.0 Safety Considerations 72.1 Personal protective equipment (PPE) 72.2 Emergency equipment 72.3 Chemical spills 82.4 Key Service Quality Requirements (KSQR) 8

3.0 Laboratory Truck and Technician 114.0 QA on Location 13

4.1 Water tests 134.1.1 Ironconcentrationtest 134.1.2 Bicarbonateconcentration 14

4.2 Gel tests 144.3 Other QA tasks while pumping 15

5.0 Typical Laboratory Tests 175.1 Water analysis 17

5.1.1 pH,specificgravity,andturbidity 175.1.2 Alkalinity(indicatormethod) 205.1.3 Chloride 215.1.4 Calciumandmagnesium 215.1.5 Sulphate,barium,iron,andpotassium 235.1.6 Sodium(calculationmethod) 24

5.2 Linear fluid viscosity 255.2.1 Water-basefluidlineargelviscosity 25

5.3 Vortex closure 265.4 Fracturing fluid crosslink delay 275.5 Static gel break test 285.6 HPHT gel rheology 305.7 Fracturing sand sieve analysis 31

5.7.1 Samplingtechniques 325.7.2 Sandsieveanalysis(modifiedAPImethod) 32

5.8 Proppant turbidity test 335.9 Silt turbidity test 34

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5.10 Proppant sphericity and roundness 345.11 Fluid compatibility with RCP 355.12 Vapor pressure test 36

6.0 Hydraulic Fracturing Fluids 376.1 Linear gel 376.2 YF1xxHTD fluids 386.3 YF8xxHT fluids 406.4 YF”GO”-III fluid 416.5 YF100LG fluids 426.6 YF100LGD fluid 446.7 Crosslink delay 456.8 PrimeFRAC fluids 45

6.8.1 Crosslinkinganddelaytimes 466.8.2 RCP/PrimeFRACcompatibility 476.8.3 QA/QCforJ464L,J494L,andJ513 47

6.9 Super X emulsion 496.10 ClearFRAC J508W 50

7.0 Matrix Acidizing Fluids 517.1 HCl 517.2 Intensified Acid 527.3 Clay acid 527.4 Mud acid 537.5 Organic mud acid 557.6 Organic clay acid 567.7 Alcoholic acid 567.8 Dynamic acid dispersion (DAD) 57

8.0 QA/QC Practices 598.1 Fracture fluid QA/QC 598.2 Fracture fluid additives QA/QC 60

8.2.1 J515 628.2.2 LGDCrosslinker 628.2.3 U028 63

9.0 References 6510.0 Check Your Understanding 67

5JET 38 - WPS-Basic Laboratory Training and Fluid QA/QC |

1.0Introduction

The fracturing fluid is a critical component of the hydraulic fracturing treatment. Its main functions are to open the fracture and to transport propping agent along the length of the fracture. To make sure that the fluid and proppant pumped is of the best quality and to maintain the quality during the treatment, the laboratory technician must perform a variety of tests. This module introduces basic field and laboratory tests that employees performing the fluid tests should know.

1.1 Learning objectivesThe objective of this manual is to introduce you to Well Productivity Services (WPS) basic lab training and fluid QA/QC. After reading this manual, you should be able to do the following:

Perform water analyses.

Understand Fann® Model 35 viscometer operation and perform gel viscosity measurement.

Understand the vortex closure test.

Perform the fracturing fluid crosslink delay test.

Perform the static gel break test.

Understand Fann Model 50-type viscometer operation and perform an HPHT gel rheology test.

Perform sand sieve analysis.

Prepare hydraulic fracturing fluids.

Prepare matrix acidizing fluids.

Understand fracturing fluids QA/QC.

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6 | Introduction

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2.0 SafetyConsiderations

All employees working in fracturing laboratory must follow specific rules and procedures to prevent injuries and loss of equipment.

All Well Services (WS) and Oilfield Services (OFS) safety standards must be complied with. All personnel should review Well Services Standard 24, Laboratory Operation, InTouch Content ID# 3313702.

2.1 Personal protective equipment (PPE)Proper personal protective equipment (PPE) should be worn while working in the laboratory.

eye protection

Safety glasses with fixed side shields are required at all times as minimum eye protection (this requirement does not apply to offices, restrooms, or other protected areas not in the laboratory working area).

Indirect vented chemical goggles must be worn when handling chemicals such as cement, unless these chemicals are in sealed containers.

Face shields must be worn when handling hot liquids, acids, or liquids that are under pressure, or working with flammable liquids where the flash point is less than 100 degF.

Visitors must wear safety glasses with side shields while in the laboratory work areas.

protective clothing

Laboratory coats with long sleeves must be worn as the minimum protective clothing.

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Rubber or plastic protective aprons must be worn, depending on the type of chemical. Read the MSDS for each chemical for the protective clothing requirements.

Types of clothing that allow exposure to a large area of skin must not be worn in a laboratory (e.g., sleeveless tops, short skirts, or short pants).

other requirements

Safety boots are not required in the laboratory. Shoes that provide protection from liquids must be worn, such as a leather shoe that covers the foot. Sandals and open shoes are not permitted.

Gloves must be worn when handling chemicals, according to the MSDS.

Please refer to SLB QHSE Standard S003, Personal Protective Equipment, InTouch Content ID# 3260259, for more information.

2.2 Emergency equipmentThe following lists the emergency equipment that must be available.

Every WS laboratory must have at least one eyewash station and one emergency shower.

Fire extinguishers must be easily accessible in case of fire.

Every laboratory must have a complete first aid kit.

Fire blankets must be available in any laboratory where tests are performed with flammable liquids.

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8 | Safety Considerations

Chemical spill control kits are necessary for the laboratory. The kits must include rubber gloves, absorbent material or spill booms, disposal bags or containers with labels, and a mercury spill control kit, if mercury is used in the laboratory.

Laboratories must have easy access to exits so that personnel can leave the laboratory in case of a fire.

Emergency numbers and procedures must be displayed at the entrance to the laboratory.

2.3 Chemical spillsThe following lists the precautions that must be taken for chemical spills.

Each laboratory and laboratory field van must be equipped with the spill disposal kit.

A spill response plan should be prepared that follows this general outline:

Make sure all personnel are removed from the area.

If flammable or combustible fluids are used, shut off or remove all possible sources of ignition.

Stop the chemical discharge.

Apply absorbent material to control all free liquids and place any mate-rial into a disposal container found in the spill disposal kit.

Add a label to the disposal container that shows the contents and date.

Place the container with other chemicals ready for disposal.

Report the spill to the health, safety, and environment (HSE) representative.

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Chemicals must not be put into a sink drain or any drain that is connected to a sewer or waste water drainage system.

All drain pipes must comply with local regulations. The contents of all drains must be analyzed every 12 months. The data must be recorded and kept on file.

Please refer to WS Safety Standard 24, Section 11.2, for instructions for mercury spills.

2.4 Key Service Quality Requirements (KSQR)

It is crucial to follow the Fracturing Key Service Quality Requirements (InTouch Content ID# 4147789) for successful job preparation and execution.

The following points specify the laboratory operations:

Design and preparation requirements

Follow proper lab procedures. Responsible: LM

Perform base fluid lab testing on any of the following applications: jobs above 82 degC [180 degF]; new client; new formation; new technology or new product. Testing to include breaker testing (schedule generation and verification) completed prior to job at bottomhole temperature and Fann 50 for cross-linked fluids. Responsible: LM

Verify chemical load out volumes and additive calculations before loading the job. Responsible: LM, JS

Follow documented loading and sampling procedures for the fracturing fluid systems being used. Responsible: LM, JS

Reverify chemical volumes and additive calculations before transporting to the wellsite or wellsite storage. Responsible: LM, JS

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Line management conducts with the JS a job brief/review/discussion that includes discussion/completion of:

SQ risk assessment

job design and procedure

job sheet with relevant well information.

Responsible: LM

Wellsite execution requirements

Crew has and uses proper and functional personal protective equipment (PPE). Responsible: JS

Conduct prejob meeting with client representative, crew, and involved third parties to agree on job procedure, design, calculations and Service Quality contingency plans. Responsible: JS

Rig up in compliance with QHSE standards. Responsible: JS

Record critical job parameters (density, rate, pressure/s, liquid additives). Responsible: JS

Perform mass balance requirements. Responsible: JS

Perform sample requirements and onsite fluid QA/QC requirements. Responsible: JS

Pump the job as designed. Any deviation from original job procedure requires agreement with client representatives. Responsible: JS and LM.

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10 | Safety Considerations



3.0 LaboratoryTruckandTechnician

A laboratory truck (Fig. 3-1) or similar dedicated laboratory unit, equipped with basic fluid quality testing tools (Fig. 3-2) must be present at the job site during a fracture treatment.

Figure 3-1. Field Laboratory Truck

Figure 3-2. Field QA/QC Kit

Mud balance

Water bath Balance

Digital titrator

Retort kit

Hydrometers Graduated cylinders Syringes Flasks Beakers Sample bottles

Stopwatch

Process controlled rheometer

Variable speed mixer

Emulsion stability meter

Conductivity meter Remote laser thermometer Dry probe pH meter

Reagents

Production screen tester

Field QA/QC kit

Bacteria luminometer

12 | Laboratory Truck and Technician

Fluid samples gathered from the field blending equipment, or fracture tanks if batch mixed, are checked for quality control. On land-based fracture treatments, the fluid is most often mixed in a PCM* precision continuous mixer and supplied to a POD* programmable optimum density blender. The quality assurance (QA) that can be performed with this truck in the field lab ensures that the treatment is executed as designed. Simple QA steps can greatly increase the odds of success for a hydraulic fracturing treatment.

The laboratory technician (Fig. 3-3)

works under the direction of the job supervisor to collect samples and perform fluid quality control

must understand the principles of stimulation and fluid rheology

must be able to calculate and prepare solution concentrations and additives

checks the quality of the water before gel is prepared

collects samples for testing and troubleshoots all problems of hydration, gel loading or crosslinking.

Figure 3-3. Laboratory Technician Hard at Work

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4.0 QAonLocation

The following are QA tasks that will need to be performed on location before pumping the stimulation treatment.

4.1 Water testsTests must be performed on the mix water for

temperature

pH

specific gravity–hydrometer method

iron concentration

bicarbonate concentration.

You will need a sample of water from each tank (3 to 5 L). At least 1 L of water should be reserved in case additional testing is necessary in the district laboratory after the fracture, such as in the case of a screenout.

Test the water parameters to ensure that they are within the range of acceptable values for the fluid pumped.

4.1.1 Iron concentration testPerform this test as follows, using a HACH iron test kit:

STEP 01 Insert the iron color disk into the comparator.

STEP 02 Fill a clean color test tube to the 5-mL mark and then add the chemical packet to the tube and shake to mix. An orange color will develop if iron is present.

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STEP 03 Insert the tube of prepared sample into the right top opening of the comparator.

STEP 04 Fill the other color viewing tube with an untreated water sample. Place it in the left top opening of the color comparator.

STEP 05 Hold the comparator up to a light source and view through the openings in front. Rotate the disc to obtain a color match. Read the mg/L iron (Fe) concentration through the scale window.

STEP 06 If the concentration is greater than 10 mg/L, perform another test with a diluted sample as follows:

Use a 1-mL sample of water to be tested and 4 mL of distilled water.

Follow the procedure in Steps 1 through 5, but multiply the results by 5.

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14 | QA on Location

4.1.2 Bicarbonate concentrationFollow this procedure to test for bicarbonate concentrations.

STEP 01 Measure 100 mL of undiluted sample into a 300-mL glass beaker.

STEP 02 Insert a clean delivery tube into the titration cartridge (1.6N H2S04). Attach the cartridge to the titrator body.

STEP 03 Hold the digital titrator with the cartridge tip pointing down. Turn the delivery knob to eject air and a few drops of titrant.

STEP 04 Reset the counter to zero and wipe the tip.

STEP 05 Add the contents of one Bromocerol green-methyl red indicator powder packet to the glass beaker and swirl to mix.

STEP 06 Titrate with sulfuric acid to a light pink color. As the titration progresses, the colors will change from light greenish blue-gray to light pink.

STEP 07 Record the value shown on the digital titrator as the total bicarbonate (the units are in mg/L as CaCO3).

4.2 Gel testsThe linear gel must be tested before beginning the job. A linear gel sample prepared with the actual water and chemical samples on location must be mixed and analyzed before job fluid mixing commences. Use the procedure detailed in Section 6-1, check the viscosity of the gel using the Fann 35-type viscometer and compare the tested viscosity and temperature with the expected ranges. When this sample meets the specification, begin initial mixing

with the PCM or GelSTREAK and perform the following tests.

STEP 01 Measure the pH of the linear gel and record.

STEP 02 Divide the linear gel into 2 beakers of 250 mL each.

STEP 03 Make a crosslinked solution using volumes recommended in laboratory testing.

STEP 04 Start the mixer at a low speed and add the chemicals.

STEP 05 Measure and record the time it takes for the fluid to have a vortex closure in the mixer and the time it takes for the fluid to have a good hang lip (crosslink).

STEP 06 Test and record the pH of the crosslinked fluid.

STEP 07 Borate fluid systems only: Perform a shear test of the fluid by submitting it to high speeds in the mixer and ensuring that the fluid will heal itself after shear.

STEP 08 Perform a breaker test at bottomhole temperature (BHT). Use concentrations dictated by the latest laboratory report to add the correct amount of breaker to a beaker of crosslinked gel. Place the sample into a water bath at bottomhole temperature. Test and record the time until the gel starts to break.


4.3 Other QA tasks while pumpingThe following are common QA tasks while pumping:

Throughout the job, linear gel should be continually checked for viscosity and temperature to confirm the proper gel loading.

Samples should be taken from the outlet of the blender or fracture pumps to test the delay time of the crosslinked fluid as well as pH, temperature, BHT stability, and break testing (water bath).

The physical quantities of all liquid and dry additives should be continually checked throughout the job to compare to the designed amount to be pumped.

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16 | QA on Location



5.0 TypicalLaboratoryTests

Several tests are commonly performed at the district laboratory before the job.

5.1 Water analysisThe oil industry uses water analysis for quality control, formation identification, compatibility studies, and environmental evaluations.

The following procedures have been developed to perform the necessary water analyses.

pH testing (meter)

specific gravity testing (hydrometer and SG bottle method)

turbidity testing (HACH method)

5.1.1 pH, specific gravity, and turbidityThe following describes how to test water for pH, specific gravity, and turbidity.

You will need the following items:

pH meter and calibration fluids

SG bottle

balance

filtering apparatus and accessories (filter paper, vacuum pump and funnel assembly)

deionized (DI) water

water sample

Filter the sample if not clear by observation. Save the filtrate for further analysis.

Follow the procedures in the following sections to test the water.

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5.1.1.1 pHThe normal pH range for brines is between 6 to 8. A low pH may indicate spent acid, whereas a high pH may indicate contamination by mud or filtrate. Some of the constituents that control the pH of water are dissolved solids, precipitation of iron, carbon dioxide, bicarbonate, borate, and hydrogen sulfide. The pH of water can strongly affect the hydration of a polymer and mechanism of some cross-linking reactions. It should be tested using pH paper and a digital pH monitor.

The pH paper is appropriate for a quick check on most fluids, providing the paper is not old and has not been exposed to extreme heat or sunlight. The pH paper test procedure is very simple:

STEP 01 Dip a piece of pH paper into the water sample.

STEP 02 Match the color of the paper with the chart on the package of pH paper.

For a more accurate reading, a pH meter should be used:

STEP 01 Calibrate pH meter as described in the pH meter manual.

STEP 02 Shake the water sample to homogenize it.

STEP 03 Insert the pH probe into the water sample.

18 | Typical Laboratory Tests

STEP 04 Read the pH after the reading stabilizes on the meter screen. Check the temperature. Record the pH and temperature.

Note:The closer the pH is to 8.0, the slower the gel will hydrate.

If the pH is close to or equal to 8.0, it is recommended to buffer with acid.

If the pH is above 8.0, the water must be buffered.

If buffering the tank, add 1 galUS 36% HCl per 20,000 galUS and check the pH. If the pH is at or above 7.5, add HCl by the quart until the pH is below 7.5.

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5.1.1.2 Specific gravitySpecific gravity is the ratio of the weight of material to the weight of water, or the density of the material to the density of water. Fresh water has a specific gravity of 1.000. The higher the specific gravity is, the heavier the liquid will be. Specific gravity can be used to differentiate hydrocarbons (condensate) from water. A hydrometer is used to measure specific gravity.

Hydrometer procedure (the preferred method in the field):

STEP 01 Fill a graduated cylinder with the fluid to be tested. Use a 100-ml cylinder for a 7-in hydrometer and 250-ml cylinder for a 12-in hydrometer.

STEP 02 Carefully drop the hydrometer into the liquid with a slight spin.

STEP 03 Read the value for specific gravity where the top of the fluid intersects one of the lines on the hydrometer.

STEP 04 The value for specific gravity should be corrected for temperature by using the temperature correction table (rule of thumb: Add 0.0002 to the SG for every degree above 60 deg).

HCl strength can also be determined from its specific gravity and compared to the chart in the acid strength chart found in the Field Data Handbook.

Use this equation to relate API gravity to specific gravity:

SG= 141.5 131.5 + API

API= 141.5 – 131.5(SG) SG

Note:The higher the API gravity is, the lighter the fluid is.

SG Bottle Procedure:

Follow this procedure to determine the SG using the SG bottle.

STEP 01 Weigh the empty SG bottle and record the weight as W1.

STEP 02 Fill the bottle with DI water until water runs out of the capillary and cap it.


STEP 03 Weigh the bottle containing DI water and record the weight as W2.

STEP 04 Clean the bottle to be used for the water sample three times, fill it with the water sample, and cap it.

STEP 05 Weigh the bottle containing the water sample and record the weight as W3.

STEP 06 Clean everything you used for this test with DI water.

To calculate the SG of the sample water, use this formula:

SG= (W3 – W1) (W2 – W1)

5.1.1.3 TurbidityMake sure to use unfiltered water for this test.

STEP 01 Switch on the HACH2000 spectrophotometer (Fig. 5-1) and enter the method #750.

Figure 5-1. HACH2000 Spectrophotometer

STEP 02 Adjust the wavelength to 450 nm for the test.

STEP 03 Fill a clean sample cell with 25 mL of the water sample and another clean sample cell with 25 mL of DI water.

STEP 04 Insert the DI water sample cell into the cell holder and close the shield.

STEP 05 Press ZERO to zero the machine.

STEP 06 Place the sample cell with the sample water into the holder and close the shield.

STEP 07 Press READ/ENTER to obtain the FTU water turbidity.

STEP 08 Turn off the HACH2000 and clean up the cells with DI water.


5.1.2 Alkalinity (indicator method) Fluids should be tested for alkalinity. Bicarbonates, carbonates, and hydroxide can all increase the alkalinity.

Bicarbonates are very important for fracture fluid quality control. Fracturing fluids require various bicarbonate concentrations depending on the specific fluid. High bicarbonate concentrations will tend to slow gel hydration and delay fluid crosslink. If high bicarbonate concentrations are encountered, the fluid may be treated with calcium chloride (S1), which will create calcium and bicarbonate bonding. The calcium bicarbonate will precipitate, thereby reducing the dissolved bicarbonate concentration. The precipitate will not interfere with the fluid.

The other reason to determine the bicarbonate concentration is to identify the water source. High bicarbonate concentrations may be characterized by a high pH or be an indication of carbonates present in the water.

Most formations do not contain carbonates or hydroxides. If a water sample contains carbonates and/or hydroxide, it may be a clue to a problem in the customer’s well, possibly indicating the presence of some drilling mud contamination.

Most oilfield waters contain only bicarbonates, but occasionally carbonate and/or hydroxide will be present.

Follow this procedure to test the alkalinity. Use a 50-mL sample regardless of the specific gravity.

STEP 01 Add 3 drops of phenolphthalein indicator. If the sample did not turn pink, the sample does not contain carbonates or hydroxide. Continue with Step 02.

If the sample did turn pink, continue to Step 05.

STEP 02 If the sample did not turn pink add ½ dropper methyl purple.

STEP 03 Titrate with 0.1N HCl or 0.0164 N HCl to the purple endpoint.

STEP 04 Calculate the bicarbonates concentration:

For 0.1N HCl, bicarbonates (mg/L) = mL of 0.1N HCl x 122

for 0.0164N HCl, bicarbonates (mg/L) = mL of 0.0164N HCl x 20

Note:These equations are valid only for 50-mL samples.

STEP 05 If the sample did turn pink after Step 01, titrate with 0.1 N HCl until the pink color disappears. The amount of 0.1N HCl used will be P in the calculations.

STEP 06 Add 3 drops of methyl purple.

STEP 07 If sample turns green, titrate with 0.1 N HCl to the purple endpoint. The total amount of 0.1 N HCl used in both titrations will be T in the calculations.

STEP 08 Perform the calculations indicated in Table 5-1.

Table 5-1. Alkalinity Indicators

Indicator Bicarbonates Carbonates Hydroxides

P<1/2T T-2P 2P None

P=1/2T None 2P None

P>1/2P None 2(T-P) 2P-T

P=T None None T

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P = amount of 0.1 N HCl required to titrate sample to a colorless endpoint after adding phenolphthalein

T = amount of 0.1 N HCl required to titrate sample to colorless endpoint after adding phenolphthalein plus the amount of 0.1 N HCl required to titrate sample to the purple endpoint after adding of methyl purple.

bicarbonate (mg/L) = (mL of 0.1N HCl) (122)

carbonates (mg/L) = (mL of 0.1N HCl) (60)

hydroxides (mg/L) = (mL of 0.1N HCl) (34).

5.1.3 ChlorideMost fracture fluids today contain 2% KCl. The chloride content of a 2% potassium chloride solution should be approximately 9,600 mg/L.

The chloride test can also be used to determine if a sample is spent acid. The characteristics of spent acid are a high chloride content and a pH of approximately 3.0 to 6.0.

STEP 01 Check SG to determine proper sample size according to Table 5-2.

Table 5-2. SG of Fluid vs. Amount of Sample

Specific Gravity Amount of Sample

1.000to1.003 50mL

1.003to1.020 10mL

1.020andover 1mL

STEP 02 Dilute to 50 mL with distilled water.

STEP 03 Add 3 to 4 drops of potassium chromate.

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STEP 04 Titrate to the orange/red endpoint with 0.1N silver nitrate.

Note:If a sample contains H2S (it will have a rotten egg smell), heat the sample until the odor is eliminated.

STEP 05 Perform the following calculation:

Cl(mg/L)= (3545)(mL of silver nitrate) sample size (mL)

For concentrations of silver nitrate other than 0.1N, use this calculation:

Cl(mg/L)= (mL of silver nitrate)(normality of silver nitrate)(35,500)

sample size

5.1.4 Calcium and magnesium The following sections describe how to determine the calcium and magnesium content in the water. Magnesium and calcium are the most common sources of hardness in produced waters; any other components that may contribute to total hardness are negligible.


5.1.4.1 CalciumMost produced water will have less than 15,000 mg/L of calcium. If higher concentrations of calcium are encountered, the water is almost certainly from a limestone or dolomite formation that has recently been acidized. If less than 15,000 mg/ L calcium is detected, continue the water analysis.

Follow this procedure to determine the calcium content.

STEP 01 Determine the correct sample size. The sample size depends on the SG of the fluid; see Table 5-3.

Table 5-3. Amount of Sample vs. Specific Gravity

Specific Gravity Amount of Sample

1.000to1.003 50mL

1.003to1.020 10mL

1.020andover 1mL

STEP 02 Dilute the sample (if less than 50 mL) to 50 mL with distilled water.

STEP 03 Add 3 to 4 drops NH4OH.

STEP 04 Add 2 scoops of Calver II hardness reagent.

STEP 05 Titrate with 0.025 M EDTA to the blue endpoint.

STEP 06 Perform the following calculations:

Ca(mg/L)= (mL of 0.025 MEDTA used)(1,000) sample size

For EDTA concentrations other than 0.025 M, use this equation:

Ca(mg/L)= (mL EDTA used)(molarity of EDTA)(40,100) sample size

5.1.4.2 MagnesiumThe magnesium test used (standard titration method) is a test for total hardness. This test assumes that the water hardness is due to dissolved magnesium and calcium only. Generally, the magnesium concentration is used for total dissolved solids calculations to identify the water source. However, high magnesium is generally due to a recent acid treatment of a dolomite formation.

The following standard titration method requires that calcium be determined before the calculating the magnesium concentration. Subtract the calcium concentration from the total hardness and assume the remaining hardness is due to magnesium.

Follow this procedure:

STEP 01 Determine correct sample size.

STEP 02 Dilute to 50 mL with distilled water.

STEP 03 Add 3 to 4 drops NH4OH.

STEP 04 Add 2 scoops of Univer II hardness reagent.

STEP 05 Titrate with 0.025 M EDTA to the blue endpoint.


Note:This test is for the total hardness. To find the amount of 0.025 M EDTA for magnesium, subtract the number of mL of 0.025 M EDTA used to determine calcium. This difference is the number of mL of 0.025 M EDTA used to determine the magnesium.

STEP 06 Perform the following calculation:

Mg(mg/L)= [(mL of 0.025 MEDTA for Mg) – (mL of EDTA for CA)](606)

sample size

For EDTA other than 0.025 M, calculate

Mg(mg/L)= [(mL of 0.025 MEDTA for Mg) – (mL of EDTA for CA)](molarity EDTA)(24,340)

sample size

5.1.5 Sulphate, barium, iron, and potassium

To test the quantity of sulphate, barium, iron, and potassium in the sample using the HACH2000 spectrophotometer, you will need the following items:

HACH2000 with accessories

DI water

SulfaVer® Reagent Powder Pillow for SO42-

BariVer® 4 Reagent Powder Pillow for Ba2+

FeroVer® Iron Reagent Powder Pillow, for Fe2+/Fe3+

potassium I/II/III reagent, for K+

water sample.

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Follow these procedures.

STEP 01 Switch on the HACH2000.

Repeat Steps 02 through 14 for each contaminant being tested for.

STEP 02 Enter the appropriate stored program number (680 for sulphate, 20 for barium, 265 for iron, and 950 for potassium).

STEP 03 Rotate the wavelength dial until the display shows 450 nm for sulphate or barium, 510 nm for iron, or 650 nm for potassium.

STEP 04 Press READ/ENTER.

STEP 05 Pour 25 mL of sample into the sample cell.

STEP 06 Add the contents of appropriate reagent powder pillow to the sample cell (the prepared sample). Swirl to dissolve.

STEP 07 Press SHIFT TIMER.

STEP 08 When the timer beeps, fill another sample cell (blank) to 25 mL of sample. Place it into the cell holder and close the light shield.

STEP 09 Press ZERO to zero the machine.

STEP 10 Within a few minutes after the timer beeps, place the prepared sample into the cell holder. Close the light shield.

STEP 11 Press READ/ENTER.

STEP 12 Record the reading.


STEP 13 Dilute the sample if the reading flashes (over limit) and repeat the above procedures.

To determine the quantity of the contaminant, use the following equation.

contaminant content (mg/L) = HACH2000 reading × dilution factor (if any)

5.1.5.1 Iron (HACH method)When high iron is encountered in fracture fluid mix water, breaker J218 (ammonium persulfate) will have an accelerated effect. In high iron environments, J218 may cause premature breaking of the fracture fluid.

In addition, high iron content will interfere with the crosslinking of the fracture fluid, resulting in poor crosslink integrity.

The maximum iron concentration for fracturing water ranges from 8 to 25 ppm, depending on the fluid.

You will need a CHEMetrics kit.

Follow this procedure to determine the iron content.

STEP 01 Fill the dilutor snapper cup to the 25 mL mark with iron-free water.

STEP 02 Fill the microtest tube halfway with your sample.

STEP 03 Holding the VACUette almost horizontally, touch the tip to the contents of the micro test tube. The tip fills completely by capillary action.

STEP 04 Completely immerse the VACUette tip into the contents of the dilutor snapper cup. Snap the tip of the ampule and wait until the VACUette fills up. The sample

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fills the ampoule and begins to mix with the reagent.

Note:A small bubble of inert gas will remain in the ampoule to facilitate mixing.

STEP 05 Remove the VACUette from the dilutor snapper cup. Mix the contents of the VACUette by inverting it several times, allowing the bubble to travel from end to end each time.

STEP 06 After 1 min, use the appropriate comparator to determine the level of iron in the sample.

5.1.6 Sodium (calculation method)To determine the sodium content of the water using the results of the tests described in Sections 5.1.1 through 5.1.5, use this equation:

mg/L of Na+ = 23 × (A/35.5 + B/61 + C/60 + D/17 – E/56 – F/137 – G/24 – H/40 –I/39)

where

A = chloride (mg/L)

B = bicarbonate (mg/L)

C = mg/L of carbonate (mg/L)

D = mg/L of OH- (mg/L)

E = mg/L of iron (mg/L)

F = mg/L of barium (mg/L)

G = mg/L of Mg2+ (mg/L)

H = mg/L of Ca2+ (mg/L)

I = mg/L of K+ (mg/L).

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5.2 Linear fluid viscosity To determine the viscosity of linear fluids (in-cluding water-based fracturing fluids, gelled oils, and gelled acids), the Fann® Model 35 rheom-eter (Fann 35) is primarily used.

Follow these practices to calibrate the rheometer:

Perform a full calibration Monday of each week or each 75 hours of operation, whichever comes first.

The rheometer must be cool and clean.

The rheometer must agree with the calibration oil chart to within ±1 cP.

If the rheometer does not calibrate, then service the unit or send out for repair as instructed by the instrument manual.

After each test, do the following:

Take off rotor and bob. Clean each piece with soap and water.

Wipe off the shaft with a damp cloth in a down motion. Do not press against the shaft-up motion pushes fluid up the shaft.

Reassemble unit ensuring that each piece is finger-tight. Tightening the bob or the rotor too much can damage the shaft and torque transducer.

5.2.1 Water-base fluid linear gel viscosityYou will need the following items:

Fann 35 viscometer with appropriate parameters (speed factor, R-B factor and spring factor)

rotor and bob

Fann 35 sample cup

fracturing fluid

thermometer

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water sample.

The approach is to hydrate the polymer following the Fracturing Materials Manual (InTouch Content ID# 4223817) procedures, sample the fluid, load the fluid into the Model 35 sample cup, and record the bob deflection at different rotor rotational speeds. Generally six rpms are available: 3, 6, 100, 200, 300, 600 rpm.

STEP 01 Power on the Fann 35.

STEP 02 Install the rotor and bob if they are not in there already.

STEP 03 Fill the sample cup to the mark with fracturing fluid.

STEP 04 Place the sample cup on the stage. The three pins on the bottom of the cup sit in three holes on the stage.

STEP 05 Raise the stage until the sample cup is at the mark on the rotor.

STEP 06 Set the Fann 35 to the desired shear rate.

Note:Shift gears only when the instrument is running.

STEP 07 Let the dial come to a steady reading and record the reading.

STEP 08 Measure and record the fluid temperature.

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STEP 09 Compare the reading with the appropriate hydration curve. All laboratories and laboratory trucks should have the hydration curves onsite; you can also find them in the Fracturing Materials Manual, InTouch Content ID# 4223817.

Allow gel to hydrate for an additional 10 min if the viscosity is 95% of the nominal value.

Verify the pH and water temperature are within the prescribed limits.

Add polymer in 2-ppt increments if the viscosity is still low after 10 additional minutes of hydration and the pH and water temperature are within specifications.

5.3 Vortex closure Vortex closure is one method for estimating a crosslink time, as are the crosslink delay temperature and crosslink delay time tests. But, whereas the crosslink delay temperature or crosslink delay time tests indicate the time or temperature required to achieve a lipping fluid, the vortex closure test simply indicates the onset of viscosity development (and rarely coincides with full crosslinking).

There are three distinct fluid behaviors during a vortex closure test:

The first is the linear fluid behavior. This is the initial state of the fluid and is characterized by a deep vortex.

The second is the viscosity increase that results in vortex closure, but does not stop fluid circulation in the blender cup.

The third behavior is fluid crowning, which is the formation of a dome of fluid over the center of the blender cup (over the blades). This is the point at which the fluid no longer completely circulates in the blender cup. It indicates

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crosslinking has occurred and an elastic lipping material has formed.

It is important to determine the time to both vortex closure and fluid crowning during a vortex closure test.

Note:Continuing to shear the fluid after vortex closure will degrade the thermal stability and appearance of the gel. Therefore, you must prepare a new fluid sample for breaker tests or for baseline fluid performance characterization; do not use the same fluid sample from which the vortex closure and crowning times are determined.

To perform this test, you will need the following items:

Waring blender

timer

fluid to be tested, including all additives

crosslinker to be tested.

Follow these procedures to perform the vortex closure test.

STEP 01 Prepare 250 mL of the base fluid (KCl or L64, surfactants, stabilizers, and buffers for polymer fluids; the fracturing oil and the recommended additives for gelled oils). Include all additives except the crosslinker.

STEP 02 Add the base fluid to a 1-L glass Waring blender cup. Adjust the mixing speed to develop a deep vortex. The top of the blade nut should just be visible, but the flats of the blade should not be covered in the fluid.

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STEP 03 Simultaneously add the crosslinker/activator package and start a timer.

STEP 04 Record the time at which the vortex closes. At vortex closure, the fluid will still be circulating in the blender and will appear to fold away from the blender sides into the center of the cup. There may still be a depression in the fluid surface at the center of the cup, but the vortex that remains is very little.

STEP 05 Continue mixing the fluid. Record the time at which the fluid surface stops moving and forms a small dome at the center of the blender cup. This time is the crowning time.

5.4 Fracturing fluid crosslink delay Crosslinking is a chemical reaction allowing a continuous, 3D structure to form in a fluid under the right conditions. Crosslinking reactions are delayed to reduce friction pressure during pumping and to reduce the time a crosslinked fluid is exposed to high shear rates. Most metal-crosslinked polymer fluids are irreversibly destroyed when they are exposed to high shear rates after crosslinking.

The delay between adding the crosslinkers and the actual crosslinking is the crosslink delay time. Any factor that affects the dissolution rate (such as temperature, concentration, shear rate, particle size distribution) will change the crosslink delay. Typically, fluids that use dissolving particles are time delayed.

It is also possible to add additives that interfere with the interaction between the crosslinker and the polymer until the fluid temperature increases. The temperature at which crosslinking will occur is called the crosslinking delay temperature.

Note:Most temperature-activated fluids will still crosslink at low temperatures after some time.

To test the crosslinking delay and the crosslinking delay temperature, you will need the following items:

Waring blender

4 plastic cups

glass beaker

pH meter

thermometer

timer

fluid sample.

There are numerous ways to determine the crosslink delay time and crosslink delay temperature of hydraulic fracturing fluids. Unfortunately, the most commonly employed methods are highly subjective. This JET manual outlines the basic procedures used for these subjective tests.

Note:Be careful to follow these procedures exactly. Subtle differences in the initial conditions and the mixing steps will change the results.

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Sample preparation

You will repeat the following steps to prepare samples for the crosslink delay time and the crosslink delay temperature tests.

STEP 01 Prepare 250 mL of the fracturing fluid following the procedure set forth in the relevant section of the Fracturing Materials Manual.

Note:Do not add the last ingredient (typically the crosslinker and/or buffer) until the initial fluid temperature and pH are measured.

STEP 02 Measure the initial fluid temperature and pH, and record these values.

STEP 03 Add the last ingredient, probably the crosslinker and/or buffer, to the fracturing fluid and mix in the Waring blender at 2,000 rpm for 30 sec. The crosslink delay time measurement starts as soon as the last ingredients are added to the fluid; record this time. Measure the final fluid pH during this step.

Crosslink delay temperature

Follow these steps to determine the crosslink delay temperature.

STEP 01 Transfer the entire contents of the blender cup into a glass beaker. Place the beaker into a microwave oven and heat the fluid for 10 sec.

STEP 02 Remove the cup and briefly stir the fluid with a thermometer at a rate similar to whipping eggs with a whisk. Then, allow the thermometer to equilibrate with the fluid and

record the temperature. Take 15 sec or less for this mixing and temperature measurement step.

STEP 03 Repeat Steps 01 and 02 as necessary. Record the temperature at which the following three characteristics are evident.

Initially, the fluid begins to thicken. It may remain linear or it may become stringy and cling to the thermometer. However, it manifests this stage, the fluid is now substantially more viscous than the linear gel was. Some call temperature at which this point is reached the initial crosslink temperature.

The fluid can support a pencil-thick tongue hanging off the edge of the beaker. The point at which it is possible to pull the tongue back into the beaker is the crosslink temperature. This is the temperature that should be used for designing the crosslink delay temperature for treatments.

The fluid becomes dry (usually) and can support a broad, thick tongue hanging off the edge of the beaker. The temperature at which this occurs is the full dry crosslink temperature.

5.5 Static gel break testThe static gel break test determines the time at which the gel breaks enough to flow back. A gel is usually considered broken enough to flow back when it has degraded to a viscosity of 20 cp at the required temperature. This test is important for the field operation that does not have high-pressure, high-temperature (HPHT), gel break test equipment.

To perform the static gel break test for any temperature, you will need the following items:

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1,000 mL jar with cap

200 mL high temperature bottles

HPHT fluid loss cell and heating jacket

Fann 35 rheometer with proper accessories

water bath with temperature control

thermometer

stop watch

gel and breaker sample.

Follow these test procedures for temperatures less than 100 degC.

STEP 01 Prepare the base gel.

STEP 02 Place the required amount of breaker solution into the linear gel before adding the crosslinker solution. Dissolve J218 or J481 into a small amount of water; use equivalent amounts of J218 and J481 if J475 and J490 Encap-breaker are used and refer to the Fracturing Materials Manual, InTouch Content ID# 4223817, for the Encap breaker release rate.

STEP 03 Crosslink the gel according to fluid preparation procedures that are published for that particular gel.

STEP 04 Preheat the water bath to the required temperature.

STEP 05 Pour 500 mL of gel into the jar. Replace the cap.

STEP 06 Place the jar containing the gel in the water bath that will bring the sample to the required temperature. Stir it slowly while heating, to accelerate the crosslinking process.

STEP 07 Start the timer when temperature reaches the indicated bottomhole temperature (BHT).

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STEP 08 Tighten the cap.

STEP 09 Shake the jar vigorously every 30 min and visually observe the viscosity.

STEP 10 Install the Fann 35’s rotor, bob, and sample cup. Heat the sample cup.

STEP 11 Take enough of the gel from the jar to fill the sample cup and place it into the heated sample cup.

STEP 12 Place the thermometer into the sample.

STEP 13 Watch the thermometer closely. Start testing the fluid viscosity at 170 sec-1 as quickly as possible when the fluid temperature is at the required temperature (the BHT). The Fann 35 does not have heating capabilities, so the sample should be heated to BHT in the water bath.

STEP 14 Continue the process in step 03 until fluid viscosity reaches 20 cp. Write the time required to reach this viscosity, which is the static gel break time.

Follow these test procedures for temperatures greater than 100 degC, using a HPHT fluid loss cell.

STEP 01 Prepare the base gel.

STEP 02 Place the required amount of breaker solution into the linear gel before adding the crosslinker solution. Dissolve J218 or J481 into a small amount of water; use equivalent amount of J218 and J481 if J475 and J490 Encap-breaker are used, and refer to FMM for Encap-breaker release rate.

STEP 03 Crosslink the gel according to the fluid preparation procedures.

STEP 04 Preheat the heating jacket to the required bottomhole static temperature (BHST).


STEP 05 Place the crosslinked gel into the bottle and finger-tighten the cap. Put the bottle with the sample into the HPHT cell containing the proper level of oil just below the bottle cap connection, to avoid oil getting into the bottle and contaminating the fluid. Keep the whole cell assembly vertical while putting the bottle into the HPHT cell.

STEP 06 Place the HPHT cell assembly with bottle/oil heating medium into the heating jacket; again, keep all components vertical.

STEP 07 Start the timer when the HPHT cell temperature reaches the indicated BHT.

STEP 08 Visually observe the viscosity of the fluid by cooling down the cell and taking out the bottle at the expected breaking time. Using your laboratory experience, determine whether it has broken or not. If it doesn’t break, you will have to repeat the test with more breaker.

5.6 HPHT gel rheology A Fann Model 50-type viscometer is used for performing a crosslinked gel breaking test when a BHT above 100 degC is required (see Fig. 5- 2).

Figure 5-2. Fann Model 50 Viscometer

To perform this test, you will need the following items:

Fann Model 50-type viscometer with appropriate parameters (speed factor, R-B factor, and spring factor)

rotor and bob-5 or bob-5X. Different bobs will have different shear rate ramps. For example, shear rate ramp corresponds to 118 rpm, 88 rpm, 59 rpm, 88 rpm, and 118 rpm with a B5 bob.

fracturing fluid sample.

Follow these test procedures. They could vary with different types of machine.

STEP 01 Power on the viscometer and its computer.

STEP 02 Supply water and N2 (usually at 450 psi, or 800 psi for Encap-breaker) after the machine is calibrated properly.

STEP 03 Prepare the crosslinked fracturing fluid as described in the specific fracturing fluid laboratory preparation procedures.

STEP 04 Activate the viscometer computer program and select Operating Menu, then Heat Bath. Type in the required temperature to start preheating the oil bath.

STEP 05 Place about 26 mL (for a bob- 5) of the crosslinked gel inside the rotor cup, followed by the required amount of breaker.

STEP 06 Place approximately 26 mL more of the crosslinked gel into the rotor cup.

STEP 07 Screw the bob counterclockwise to the shaft until it is finger tight.

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STEP 08 Slowly screw the rotor containing the sample to the expansion fitting until it is finger tight.

STEP 09 Take off the cover of the oil bath and close the glass door.

STEP 10 Go to the Operating Menu, and then Custom (or API). The API ramp should be one of the following:

118 rpm (100 sec-1)

88.5 rpm (75 sec-1)

59 rpm (50 sec-1)

29.5 rpm (25 sec-1)

59 rpm (50 sec-1)

88.5 rpm (75 sec-1)

118 rpm (100 sec-1).

STEP 11 Choose bob5, interval stir rate (118 rpm), and final temperature setpoint.

STEP 12 Click Initial test in the operating menu followed by Yes and OK to go to ASCII FILE and report printout. Choose the options you need.

STEP 13 Follow the screens through until Perform Test appears; click it.

STEP 14 The instrument will automatically run until the program finishes and prints out the results.

STEP 15 If you want to stop the machine during testing, go to the operating menu and select Shut down.

STEP 16 Click on the file on the top of screen and find the reprint report. Click it to print out the report manually.

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STEP 17 Allow the machine to cool down below 100 degF. Release the pressure and close the water line.

STEP 18 Dissemble the rotor cup and bob gently and clean them up using the recommended cleaner.

STEP 19 Turn on the nitrogen to 10 to 20 psi to get all excess water or gel residue out of the expansion fitting.

STEP 20 Spray some WD40 on the shaft to lubricate the bearing. Use a paper towel to wipe the moisture and gel off the shaft very gently (do not press against the shaft). Clean everything used and cover the oil bath.

STEP 21 Turn off the machine and release the pressure in the main nitrogen line.

5.7 Fracturing sand sieve analysis The sand used as a proppant must be analyzed for size of the grains. You will use a series of sieves that are stacked in a specified order; see Fig. 5-3.

Figure 5-3. ASTM Standard Sieves and Endecotts Sieve Shaker


5.7.1 Sampling techniques A proper sampling ensures that a representative sample of the fracturing sand is obtained for quality control testing.

delivery samples

Nine samples are needed per railroad car; 3 samples per truck load; 5 samples per 100,000 lbm when on location.

When the proper number of samples are obtained, combine the samples for one test.

conveyor belt samples

Sand falling from a conveyor belt into a truck or railcar should be allowed to flow for at least 2 minutes before catching sample; wait 2 minutes after the start of each compartment when catching location samples.

Place the sampling device in the stream of sand with its longitudinal axis perpendicular to the flowing sand. Move the sampling box at a uniform rate from side to side in the sand stream. Several samples should be extracted at uniform intervals through the body of sand and combined for a representative sample.

alternate sampling method (non-API): If a flowing sample is not possible or desired, then a grain thief may be used to obtain a sample. It is recommended to catch at least three samples whenever possible and combine them for testing.

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5.7.2 Sand sieve analysis (modified API method)

This method has been modified to meet specific criteria requested by clients. This method exceeds the API recommended practice 56 for sand sieve analysis.

STEP 01 Refer to API RP56 or Table 5-4 to determine the recommended sieve sizes used in testing designated sand sizes.

Fracturing sand size designationsUSAsievesrecommended

6/12 8/16 12/20 16/30 20/40 30/50 40/70 70/140

4 6 8 12 16 20 30 50

6 8 12 16 20 30 40 70

8 12 16 20 30 40 50 100

10 14 18 25 35 45 60 120

12 16 20 30 40 50 70 140

16 20 30 40 50 70 100 200

pan pan pan pan pan pan pan pan

Table 5-4. Recommended Sieve Sizes for Fracturing Sands

STEP 02 Establish an accurate weight (wt) of the 100-g split sample to within 0.1 g.

STEP 03 Make sure that all sieves are completely cleaned with the manufacturer-recommended brush. Weigh each sieve accurately and record the weights.

STEP 04 Stack the sieves in order of increasing mesh size from bottom to top, with the pan on the bottom.

STEP 05 Pour the sample onto the top sieve and place the sieve set plus the pan in the test sieve shaker. Cover the sieves and tighten the sieve set.


STEP 06 Power on the sieve shaker for 10 min.

STEP 07 Remove each sieve and weigh each sieve separately with its contents. Weigh the pan also.

Note:Remember to brush off the particles from the bottom of each sieve into the next size sieve before weighing either.

STEP 08 Calculate the percent by weight of the total sand sample retained on each sieve and the pan. To calculate the percentage by weight of the sand falling within the designated sieve sizes, use these equations:

weight of the retained sand (WR) = sieve weight after shaking – sieve weight before shaking

wt% of the total sand sample retained on each sieve = WR/WT x 100.

STEP 09 A minimum of 90 wt% of the tested sample should fall within the designated sieve sizes. Not more than 1.0 wt% of the total tested sand sample should be larger than the largest sieve size and not more than 1 wt% should be smaller than the smallest sieve size.

Note:The cumulative weight should be within 0.5% of the sample weight used in the test; if not, the sieve analysis must be repeated using a different sample.

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5.8 Proppant turbidity testThe turbidity test is performed to determine the cleanliness of the fracture sand (amount of fines present).

You will need the following equipment and materials:

sand sample

distilled water

glass medicine bottle graduated to 100 mL with cap

black felt tip permanent marker

small funnel to pour sand into medicine bottle.

Follow this procedure to test the turbidity:

STEP 01 Mark the flat side of the bottle with an X using the black felt tip marker.

STEP 02 Fill the bottle to the 20-mL mark with sand.

STEP 03 Add distilled water to the 100-mL mark and secure cap.

STEP 04 Shake the bottle vigorously for 20 sec.

STEP 05 In a well-lit area, hold the bottle at arms’ length with the flat side away from yourself.

If the X can be seen clearly, the sand passes the turbidity test. If the X is barely distinguishable or cannot be seen, the sand fails the test.

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Note:After the turbidity test is complete, check the pH of the sample; if the pH is above 6.0, the sand will be acceptable for YF1XX and YF2XX series fluids.

5.9 Silt turbidity testTurbidity in water is the result of suspended clay, silt, or finely divided inorganic matter being present. The HACH DR 2000 spectrometer measures the optical property of the suspension, providing a turbidity value for the tested proppant sample. The turbidity of the tested proppant sample should be 250 (FTU) formazine turbidity units or less.


HACH DR 2000-type spectrometer

sample vials

6-oz or larger, plastic-capped, widemouth bottle

syringe/pippet

DI water

proppant sample.

Follow these procedures.

STEP 01 Measure 20 mL of dry proppant sample and 100 mL of DI water in a 6-oz widemouth bottle, mix well, and allow to stand for 30 min.

STEP 02 Shake the bottle vigorously by hand for 45 to 60 shakes in 30 sec. Allow it to stand for 5 min.

STEP 03 Switch on the spectrometer.

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STEP 04 Dial the program number #750 and set the wavelength to 450 nm.

STEP 05 Zero the FTU using DI water in the test vial.

STEP 06 Using a syringe or pippet, extract 25 mL of water-silt suspension from near the center of the water volume.

STEP 07 Place the water-silt suspension in the test vial.

STEP 08 Determine the sample turbidity in FTU and record.

5.10 Proppant sphericity and roundnessParticle sphericity is a measurement of how closely a sand particle or grain approaches the shape of a sphere. Grain roundness is a mea-sure of the relative sharpness of grain corners, or of grain curvature. Figure 5-4 illustrates these concepts.

The test method is specified by API RP56 /60 (Krumbein and Sloss visual estimation method).

Figure 5-4. Sphericity vs. Roundness

Roundness

Sphe

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ty


To test for sphericity and roundness, you will need the following equipment.

optical microscope Heerbrugg, Model Wild M3 or scanning electron microscopy (SEM), Phillips, Model XL30

sample sticker/platform

proppant sample.

To perform the test, follow this procedure.

STEP 01 Stick 20 or more grains of proppant on the glass plate platform for electronic scanning electron microscope (ESEM).

STEP 02 Switch on the optical microscope. Refer to the SEM analysis for ESEM startup procedures.

STEP 03 Adjust the magnification until a clear picture of proppant particles shows up.

STEP 04 Compare the shape of the particles visually with the standard chart (see API RP56, p. 7) and determine the sphericity and roundness of each particle.

STEP 05 Record the average of the above reading as the sphericity and roundness of the proppant sample.

5.11 Fluid compatibility with RCPLaboratory testing is performed to determine the compatibility of RCP with fracturing fluids.


pH meter

water bath

Waring blender

linear gel sample

all additives

RCP sample

fluid not exposed to RCP.

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To test the fluid’s compatibility with the RCP, follow these procedures.

STEP 01 Prepare 500 mL of linear gel plus all additives except crosslinker. The crosslinker is not added for zirconate crosslinked fluids to prevent shear degradation during compatibility test.

STEP 02 Measure pH using pH meter.

STEP 03 Add 10 ppa of RCP, and mix for 30 sec at a mixer speed that creates a vortex without significantly entraining air.

STEP 04 Place the mixture in a water bath at 150 degF for 30 min.

STEP 05 After 30 min, remove the mixture from the bath and mix for 30 sec more. Stop blender and allow proppant to settle to bottom of container.

STEP 06 Transfer 250 mL of fluid (without proppant) to a clean blender. Note:

Allow fluid to cool before continuing.

STEP 07 Measure pH using pH meter.

STEP 08 Add crosslinker and perform the bench top and rheology tests described here, or use the Fracturing Materials Manual. Follow relevant quality control standard procedures.

STEP 09 Compare fluid properties and rheology profile with that of a fluid not exposed to RCP. Viscosities measured on a Fann 50-type rheometer should be similar for fluids prepared with and without RCP exposure (typically within 100 cp for same test conditions).


STEP 10 If significant loss in viscosity is observed, fluid performance may be improved by increasing the crosslinker concentration.

If significant loss in viscosity is observed—the fluid is not stable and looks broken—you will know that the fluid is not compatible with the RCP.

5.12 Vapor pressure testThe Reid method determines the vapor pressure of petroleum products. This method offers the type of data commonly requested for the field.

Warning:Keep heat and ignition sources away from the test.


sample to be tested

Note:Sample should be handled diligently to minimize vapor loss.

water bath, adjustable from 100 to 140 degF

Reid vapor pressure tester; refer to ASTM232-82 for details.

Follow this procedure.

STEP 01 Unscrew the testing chamber at its midsection and inspect the O-ring seal.

STEP 02 Transfer 25 to 30 mL of sample to the bottom half of the testing chamber and

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then quickly screw the upper and lower halves together.

STEP 03 Immerse the apparatus into the water bath and start heating. Heat bath slowly so that the sample temperature remains close to the bath temperature.

STEP 04 Using the Reid vapor pressure tester, record vapor pressure of the sample when the temperature is 100 degF. Note the exact temperature and pressure when taking a reading. Be sure to shake the test chamber vigorously before each reading to ensure that the validity of the sample has been maximized.

STEP 05 Continue heating and record the vapor pressure when the bath temperature reaches 130 degF. Note the exact temperature and pressure at the time of the reading.

STEP 06 Discard the sample and thoroughly wash the apparatus with water.

STEP 07 To find the vapor pressure, plot pressure vs. temperature of the data collected. Extrapolate to obtain the exact pressure at 100 degF and 130 degF for reporting.


6.0 HydraulicFracturingFluids

These hydraulic fluids are the fluids that the engineer designs for a particular job. They must be tested in the laboratory before pumping the job. These procedures explain preparing the fluids.

6.1 Linear gelThe linear gel (Fig. 6-1) can be prepared for all water-base fluids in this way.

Figure 6-1. Sample Linear Gel

To prepare the linear gel, follow these generic procedures.

STEP 01 Measure 500 mL of deionized (or field) water into a 1-L Waring blender cup.

STEP 02 Add either 167 ppt KCl or 2 galUS/1,000 galUS L64. You may need to stir until well mixed, depending on the specific fracture fluid.

STEP 03 Adjust the fluid pH if necessary, as per the manual guidelines for your specific fluid.

STEP 04 Add the required amount of polymer to the blender, mixing at 2,000 rpm.

STEP 05 Mix for 5 min.

STEP 06 Measure viscosity at 100 rpm on a Fann 35 with R1-B1 at 80 degF.

38 | Hydraulic Fracturing Fluids

6.2 YF1xxHTD fluidsThe Widefrac* 100HTD (YF*100HTD) fracturing fluids are water-base systems comprising a refined guar gelling agent crosslinked by a borate-type crosslinker. These fluids are designed for batch- or continuous-mix operations.

YF100HTD fluids can be used at temperatures ranging from 125 to 325 degF (52 to 163 degC).

To prepare YF1xxHTD, you will need the following items:

Waring blender equipped with variable transformer

blender jar

graduated cylinder and syringes

timer

magnetic stirrer

glass bottle, 1L

pH meter

thermometer

Fann 35-type viscometer.

You will also need the proper additives. The additives in a typical YF140HTD system can include the following (concentration amount for 500 mL):

M117 potasium chloride 166 lbm/1,000 galUS (10 g)

M275 microbiocide 0.45 lbm/1,000 galUS (0.027 g)

J353 HT gel stabilizer 10 lbm/1,000 galUS (0.6 g)

F103 surfactant 1 galUS/1,000 galUS (0.5 mL)

J424 gelling agent 40 lbm/1,000 galUS, (2.4 g)

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L10 crosslinker 7.5 lbm/1,000 galUS (0.45 g)

M2 activator 15 lbm/1,000 galUS (0.9 g)

J450 stabilizer 1 galUS/1,000 galUS (0.5 mL)

J480 crosslink delay agent in concentration to be determined

J490 encap-breaker, in concentration to be determined.

Prepare the YF1xxHTD according to the following procedure.

Prepare linear gel:

STEP 01 Pour 490 mL of water into the mixing cup. Stir with low speed.

STEP 02 Add 10 g of KCl and 0.027 g of M275 into the mixing cup.

STEP 03 Add 2.4 g of J424 slowly into the cup and control the stir rate to allow the polymer to disperse.

STEP 04 Increase the stir rate after the polymer disperses to hydrate faster.

STEP 05 Hydrate the gel for 30 to 60 min.

STEP 06 While the gel is hydrating, weigh 0.6 g of J353 and dissolve it in a small amount of water.

STEP 07 Check the fluid temperature and pH of the gel. The pH should be 6 to 8.

STEP 08 Check the fluid viscosity to see if it is in the range specified in the FMM specification. See Fann 35 test procedures in Section 5.2, Linear fluid viscosity.

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Prepare the crosslinker:

STEP 09 Put 3.7 mL of water into a glass bottle. Stir using magnetic stirrer.

STEP 10 Weigh 0.9 g of M2 and add slowly into the bottle while stirring.

STEP 11 Measure 0.45 g of L10 and add it into the bottle while stirring.

STEP 12 Add the required amount of J480 slowly while stirring, until dissolved.

STEP 13 Place 0.5 mL of J450 into the bottle.

STEP 14 Age the crosslinker solution for 60 min.

Crosslink the gel (see Fig. 6-2):

Figure 6-2. Crosslinked Gel

STEP 15 Adjust the stirring speed to create a vortex to the tip of the stirrer.

STEP 16 Add J353 solution and 0.5 mL of F103 into the mixing cup to mix 1 min.

STEP 17 Add the prepared crosslinker into the linear gel while start timing.

STEP 18 Record the time to reach the vortex closure as the vortex closure time.

STEP 19 Check the time until hang-lip happens and record this time as the hang-lip time.

STEP 20 Check the pH of the crosslinked gel and record.


6.3 YF8xxHT fluidsYF800HT fluids are temperature-activated, zirconate-crosslinked, water-base fluids that use carboxymethylhydroxypropyl guar (CMHPG) as a gelling agent. Crosslinker J515 is used to crosslink the fluids. There are two fluid designs:

YF800LPH (pH 4 to 5) for temperatures from 100 degF to 250 degF [38 degC to 121 degC]

YF800HT (pH 9 to 9.5) for temperatures from 275 degF to 350 degF [135 degC to 177 degC].

To prepare YF800HT, you will need the following equipment and materials:


jar


pH meter

thermometer

Fann 35-type spectrophotometer.

The following additives are often used in a typical YF845HT (concentration amount for 500 mL). Check that these or any others indicated are in stock.

M117 potasium chloride 166 lbm/Mgal: 10 g

M275 microbiocide 0.45 lbm/Mgal: 0.027 g

F103 surfactant 1 galUS/Mgal: 0.5 mL

J916 gelling agent 10.1 galUS/Mgal: 5.05 mL

L401 buffer: adjust to pH 6.5–7.0

J353 HT gel stabilizer 10 lbm/Mgal: 0.6 g

J464 activator 10 lbm/Mgal: 0.6 g

M2 (2%) activator 10 galUS/Mgal: 5 mL

J450 stabilizer 1 galUS/Mgal: 0.5 mL

J515 crosslinker 0.7 galUS/Mgal: 0.35 mL

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Follow this procedure to prepare the YF845HT.

Prepare linear gel:

STEP 01 Pour 490 mL of water into the mixing cup. Stir with the Waring blender on low speed.

STEP 02 Leaving the blender on, add 10 g of KCl and 0.027 g of M275 into the mixing cup.

STEP 03 Measure 5.05 mL of polymer slurry (J916) and add slowly into the cup. Control the stir rate to allow the polymer to disperse.

STEP 04 Add L401 while checking the pH of the fluid until the pH is 7.0. Record the pH.

STEP 05 Increase the stir rate to obtain faster hydration and hydrate for 30 min.

STEP 06 Check the fluid viscosity to see if it is in the specified range. Record the linear viscosity against FMM spec, the pH (6.9 to 7.1), and the temperature.

STEP 07 While the gel is hydrating, weigh 0.6 g of J353 and 0.6 g of J464. Dissolve each using approximately 2 mL of water, in separate containers.

Note:The J464 solution will be used later in this procedure.

STEP 08 After the gel hydrates to meet the specification, add the J353 solution and then 0.5 mL of F103 surfactant into the linear gel, in that order. Stir the gel for approximately 2 min, and then check the pH again.


Crosslink the gel:

STEP 09 Heat the water bath to approximately 90 degC or use a microwave oven for homogeneous heating.

Note:Using the microwave is the recommended practice.

STEP 10 Add J464 solution, M2 (2%), 0.5 mL of J450, and 0.35 mL of J515 into the linear gel. Check the pH after adding each component.

STEP 11 Continue to mix the fluid at a vortex to the tip of the stirrer for 30 sec after adding the J515. Check the fluid pH.

STEP 12 Split the prepared mixture into two equal parts of approximately 250 mL. You will use one part to perform the crosslinking test and the other part to perform the Fann 50 test.

STEP 13 Begin the Fann 50 test as soon as possible after mixing the fluid in Step 11. The time between the end of the fluid mixing and beginning the Fann 50 test should not be more than 5 min.

STEP 14 To perform the crosslinking test, place the beaker containing 250 mL of prepared gel into the water bath or microwave.

STEP 15 Shake the fluid frequently to avoid a temperature gradient from the wall of the beaker to the center of the fluid. Check the crosslink every 15 to 30 sec (adjust the time more frequently while using the microwave; especially when close to the desired temperature) while testing the fluid temperature by thermometer. Record the fluid temperature when there is a noticeable resistance to the thermometer moving into/out of the fluid.

6.4 YF”GO”-III fluid YF“GO”III* is a gelled, oil-base fluid used as a fracturing fluid for the treatment of water-sensitive formations. Diesel, kerosene, condensate, and a wide variety of crude oils can be used to prepare YF“GO”III.

To prepare the YF“GO’’III, you will need the following equipment and materials:

disposable syringes

glass or plastic beakers

magnetic stirrer

balance

Waring blender

Fann 35 viscometer

graduated measuring cylinders

water bath

J452 oil gelling agent

J601 crosslinker

J602L pH control agent

M003 breaker.

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Note:If J602 is to be used, mix 1.44 g of J602 solid in 10 mL of deionized water until it dissolves. This solution is equivalent to J602L.

STEP 01 Mix J602L and J601 at a ratio of 1:5 by volume.

Place a small glass beaker on the magnetic stirrer and add the following additives:

J602L: 2 mL

J601: 10 mL

Allow this solution to mix for at least 30 min.

STEP 02 Place 1 L of the base fluid, usually diesel, in a Waring Blender and start mixing at 2,000 rpm. Create a vortex down to the blades.

Note:Normally the base fluid is diesel containing <0.5% water because the system is water sensitive.

STEP 03 Simultaneously add the desired quantity of J452 and the activator solution prepared in Steps 01 and 02 to the edge of the vortex. The quantities required to produce 6, 7, or 8 galUS of gel per 1,000 galUS of diesel (6, 7, or 8 mL/1,000 mL) are listed in Table 6-1.

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Table 6-1. J452 and Activator for YF”GO”III Gel

J452 (mL/1,000 mL diesel)

Activator (mL/1,000 mL diesel)

6 3

7 3.5

8 4

STEP 04 Mix at 10,000 rpm for 10 min.

STEP 05 Transfer gel to a Fann 35 cup and measure viscosity developed at 170 sec-1. Table 6-2 shows the desired viscosities for 6, 7, or 8- galUS gels.

Table 6-2. Desired Viscosities

J452 (mL/1,000 mL) Viscosity (cP @ 170 sec-1 @ 21 degC)

6 100to120

7 120to140

8 140to170

6.5 YF100LG fluidsThe Widefrac* 100 (YF100LG) fracturing fluids are water-base systems comprising a refined guar gelling agent crosslinked by a borate crosslinker. They are prepared from the Waterfrac 100 fluids. YF100LG fluids are designed to crosslink quickly. The vortex closure of these fluids is 5 to 10 sec, which allows uniform mixing of all components before becoming viscous. The crosslink is fairly mature in another 10 to 20 sec.

To prepare the YF100LG solution, you will need the following equipment and materials:

Waring blender

blender cup

graduated cylinders

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disposable syringes

pH meter or paper

water gelling agent J424 or PSG polymer slurry J877.

Prepare YF100LG solution.

STEP 01 Add crosslinker L010 at 1.2 to 2.2 lbm L010/1,000 galUS WF100 fluid (0.144 to 0.264 g L010/L) depending on the temperature. For adding small quantities, a stock solution of L010 can be prepared by mixing 2.3965 g of L010 to 100 mL of distilled water.

Note:1 mL L010 stock solution per 200 mL of WF100 = 1 lbm L010/1,000 galUS WF100.

Activate crosslinker:

STEP 02 The pH stabilizer (activator solution) for fracturing temperatures less than 175 degF (79 degC) contains J494 at 12 lbm/1,000 galUS of YF fluid and M3 at 5 lbm/1,000 galUS of YF fluid. This is called a 12-5 solution.

The preferred way to add the J494 and M3 to the fluid is to prepare a 14 to 20% (wt/wt) aqueous solution and meter it in the blender. To prepare a 16% (wt/wt) 12-5 solution, first place 19 mL of deionized water in a small glass beaker on a magnetic stirrer.

STEP 03 Slowly add 2.55 g of J494 to the vortex.

STEP 04 Slowly add 1.06 g of M3 to the vortex.

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Continue mixing for 15 to 20 min until the solids have dissolved.

Note:The specific gravity of a 16% (wt/wt) solution at 75 degF is 1.131 g/cm3. An addition rate of 11.3 mL/1,000 mL of linear gel is equivalent to 12 lbm J494 and 5 lbm M3/1,000 galUS of fluid.

Prepare breaker solution:

STEP 05 A stock solution of J218 can be prepared by adding 2.3965 g of J218 to 100 mL of distilled water. Then, 1 mL J218 stock solution per 200 mL of WF100 = 1 lbm J218/1,000 galUS WF100.

STEP 06 Prepare 500 mL of WF100 base gel.

STEP 07 Add L010 to the base gel and mix at low speed for 1 min, checking to ensure that air is not trapped in the gel.

STEP 08 If J218 breaker is required, add the required amount to the vortex and mix for 1 min.

STEP 09 Set the mixer speed to 1900 to 2000 rpm and add 5.65 mL of the J494:M3 activator solution to the vortex. A vortex closure of 10 to 15 sec should be observed.

STEP 10 After 30 sec, stop the mixer and transfer the fluid to a beaker. The fluid should be fully crosslinked.

STEP 11 Check the pH of the crosslinked fluid. It should be 9.6 to 9.9 at ambient temperature. If it is not, you may have contaminated additives and will need to repeat the test with fresh additives.


6.6 YF100LGD fluidWidefrac 100LGD (YF100LGD) fracturing fluids are water-base systems containing a refined guar gelling agent (20 to 50 lbm/ 1,000 gal) crosslinked with a borate crosslinker. YF100LGD fluids can be batch-mixed or continuous-mixed. YF100LGD fluids are prepared from any of the Waterfrac 100 (WF100) fluids. Addition of crosslinker, activators and a delay agent converts the WF100 fluid to the corresponding YF100LGD fluid.

To prepare the YF100LGD solution, you will need the following equipment and materials:

Waring blender

blender cup

graduated cylinders

disposable syringes

pH meter or paper

water gelling agent J424 or PSG polymer slurry J877.

Follow these procedures to mix the solution.

Prepare crosslinker:

STEP 01 Mix the crosslinker solution according to the specific requirements. The crosslinker solution comprises the following:

water (4.5 to 7 galUS/1,000 galUS).

L010 at 5.5 to 9.0 lbm L010/1,000 galUS WF100 fluid (0.659 to 1.078 g L010/L) depending on temperature.

activator M2 (10 to 20 lbm/1,000 galUS) or U28.

stabilizer J450, typically 1 galUS/1,000 galUS (if required).

For example,

fresh water: 6 galUS (6 mL)

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L10: 7 lbm (0.84g)

M2: 16.5 lbm (1.98g)

J450: 1 galUS (1 mL)

This example solution, before the J450 is added, has a specific gravity of 1.304 at 24 degC and therefore will have an addition rate of 7.8 galUS/1,000 galUS (or 7.8 mL/1,000 mL), calculated as follows:

Crosslinker rate = (weight of crosslinker solution/1,000 galUS)/(8.34 x SG) = [(6 x 8.34) + 7 + 16.5]/(1.304 x 8.34) = 6.8 galUS/1,000 galUS with 1 galUS/ 1,000 J450 = 7.8 galUS/1,000 galUS (1.56 mL/200 mL)

Mix crosslinker delay solution:

STEP 02 The concentration of the delay agent J511 depends on the polymer concentration, mix water temperature, and the desired crosslink time The minimum J511 concentration required to prevent syneresis (over-crosslinking) at room temperature for approximately 12 hr is 10 lbm/1,000 galUS. J511 is readily soluble in water. The addition of NaOH at about 1 lbm/1,000 galUS prevents bacteria from deteriorating the J511 solution (resulting in ~pH 10). Aqueous solutions with 30 to 70% J511 present can be employed. To prepare a 30% solution containing 2.79 lbm J511/galUS, add 0.02 g of J511 to 70 mL of water and mix until it is dissolved.

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STEP 03 Add 30 g of J511 and continue mixing until all solids have dissolved. Table 6-3 can be used as a guideline for adding various quantities of J511.

Table 6-3. Quantities of J511 in YF100 LGD

Desired concentration

J511 (lbm/1,000 gal US)

Equivalent to galUS of 30% J511/

1,000 galUS of WF100

Equivalent to mL of 30% J511/200 mL

of WF100

10 3.6 0.72

15 5.4 1.08

20 7.2 1.44

25 8.9 1.78

30 10.7 2.14

Prepare breaker solution:

STEP 04 Prepare a breaker solution by adding 2.3965 g of J218 or J481 to 100 mL of distilled water.

1 mL J218 or J481 stock solution per 200 mL of WF100= 1 lbm J218 or J481/1,000 galUS WF100

6.7 Crosslink delay To determine the crosslink delay time with various concentrations of J511 present, the following procedure should be followed:

STEP 01 Place 200 mL of the prepared WF100 fluid into a Waring blender jar and record the fluid temperature.

STEP O2 Start mixing at 2,000 rpm; this speed should produce a vortex.

STEP 03 Inject the delay agent and mix for 2 min.

STEP 04 Inject the crosslinker solution and start the stopwatch simultaneously.

STEP 05 Vortex closure is defined by the crosslinked gel covering the blade nut. Record the time elapsed between injecting the crosslinker solution and vortex closure.

STEP 06 Stop the blender and pour the gel into a 250-mL beaker. Start the stopwatch.

STEP 07 Pour the fluid from one 250-mL cup to another until 80% crosslink is achieved. The 80% crosslink is defined by the floppy gel easily retracting into the cup and showing no adhesion to the wall of the cup when the gel is poured. Also, notice if the crosslinked gel can be fractured during the floppy test. Record the time elapsed from vortex closure to 80% crosslinking.

STEP 08 Continue pouring the crosslinked gel from cup to cup every 15 sec until 100% crosslinking is achieved. The 100% crosslink is defined as when the crosslink gel is poured from cup to cup, the fluid comes out in one solid mass with minimal elongation.

6.8 PrimeFRAC fluidsThe PrimeFRAC* fluids are temperature-activated, zirconium-crosslinked waterbase fluids composed of CMHPG. PrimeFRAC fluids are designed to be crosslinked with J513 in a pH range from 9.1 to 9.5 in the temperature range of 200 degF to 350 degF.



blender jar


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pH meter

thermometer

Fann 35

microwave

titrator

0.1N HCl

methyl orange indicator

phenolphthalein indicator

water

Orion Model 130A conductivity meter

fluid additives and RCP.

Follow these procedures to prepare the system.

STEP 01 Check the pH of the water. It should be 6 to 8; adjust by HCl or NaOH if not in this range.

STEP 02 Pour a small amount of water into the mixing cup. Stir with low speed. Add D047 if required.

STEP 03 Add required KCl, M275, F103, and J353 in this sequence into the mixing cup.

STEP 04 Measure polymer slurry and add slowly into the mixing cup. Control the stir rate to allow the polymer to disperse. Check the pH of the fluid while adding J488 until the fluid pH is less than 7.0; record the pH and the amount of J488 needed to reach this pH.

STEP 05 Increase the stir rate to hydrate the gel faster, and hydrate for about 10 to 15 min.

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STEP 06 Check the fluid viscosity to determine if it is in the specified range according to the Fann 35 test procedures. Record the linear viscosity against the Fracture Materials Manual specifications (170 sec-1 and 511 sec-1), pH, and temperature.

STEP 07 Continue mixing for another 5 min until the viscosity meets the specification.

6.8.1 Crosslinking and delay timesTo determine the PrimeFrac gel crosslinking and delay times, follow this procedure.

STEP 01 Fill blender with 250 mL of the prepared linear gel; shear at low speed.

STEP 02 Add J464 solution, J494 solution, and J513 into the linear gel. Check pH after adding each component.

STEP 03 Continue to mix the fluid at a vortex (to the tip of stirrer) for 20 to 30 sec after adding J513.

STEP 04 Check and record the fluid pH.

STEP 05 Split the prepared mixture into two equal parts. You will use one part to perform the crosslinking test and the other part to perform the Fann 50 test.

STEP 06 Start the Fann 50 test as soon as possible after mixing the fluid. The time between the end of mixing the fluid and beginning the Fann 50 test should not be more than 5 min.

STEP 07 To perform the crosslinking test, place a beaker containing 150 mL of prepared gel into the microwave.


STEP 08 Check the crosslinking every 5 to 10 sec while testing the fluid temperature by thermometer.

STEP 09 Write down the fluid temperature when there is a noticeable resistance to the thermometer moving into/out of the fluid (100% crosslinked). This temperature should be less than 120 degF for better fluid stability.

6.8.2 RCP/PrimeFRAC compatibilityTo determine the compatibility between the PrimeFRAC solution and the RCP, follow this procedure.

STEP 01 Fill the blender cup with 250 mL of the prepared linear PrimeFRAC gel.

STEP 02 Add required amount of J464L and J494L, mix at low speed.

STEP 03 Add 1 ppa RCP to the blender; increase mixing speed for deep vortex to shear for 2 to 3 min.

STEP 04 Add J513 into the blender in the last few seconds during shearing.

STEP 05 Let mixture settle for about 2 min.

STEP 06 Mix at 1,500 rpm for 3 to 5 min.

STEP 07 Decant the clear part of the mixture. Check pH to make sure it is in the range of 9.2 to 9.5. If it is not, adjust with J494L to meet the pH requirement and record the amount of J494L added and the final pH.

STEP 08 Put approximately 150 mL of the gel into the beaker and place it into the microwave to determine the crosslink temperature according to the procedure in Section 6.8.1. Change the concentration of

J464L and repeat the procedure if the crosslink temperature does not meet the specification of less than 120 degF. Otherwise, go to next step.

STEP 09 Put approximately 35 mL of the fluid into a beaker and add the required breaker to perform the Fann 50 tests.

STEP 10 Increase the amount of proppant added for the FracCADE design to check all loadings (for example, 2 ppa, 4 ppa, 6 ppa, 8 ppa, 10 ppa, and 12 ppa). Repeat Steps 01 through 09 to obtain a detailed relationship between the RCP loading and the gel crosslinking/gel stability.

6.8.3 QA/QC for J464L, J494L, and J513Follow these procedures to check the quality of the J464L, J494L, and J513 PrimeFrac fluids. For all these fluids, you will need the following equipment and materials:

beakers

conductivity meter

pH meter

methyl orange indicator

phenolphthalein indicator

0.1N HCl

DI water

fluid sample.

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6.8.3.1 J464L To verify the quality of J464 at 0.50 lbm/galUS, follow this procedure.

STEP 01 Dilute 1 mL of J464L sample in 50 mL of DI water.

STEP 02 Add 4 drops of methyl orange indicator and shake until the mixture is homogeneous.

STEP 03 Titrate with 0.1N HCl standard solution until the color changes from orange to pink. The endpoint should be approximately 6.7 mL.

STEP 04 Calculate the concentration:

mL of 0.1N HCl x 0.0742 = lbm of J464/galUS

STEP 05 The fluid is acceptable if the within ±10% of specification.

STEP 06 Adjust field J464L rate based on above results.

6.8.3.2 J494L To verify the quality of J494 at 1 lbm/galUS, follow this procedure.

STEP 01 Dilute 1 mL of J494L sample to approximately 50 mL of DI water.

STEP 02 Add 4 drops of phenolphthalein indicator and shake until homogeneous (turns pink).

STEP 03 Titrate with 0.1N HCl standard solution until fluid color changes from pink to colorless (endpoint, about 5.6 mL).

STEP 04 Calculate the concentration:

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mL of 0.1N HCl x 0.1786 = lbm of J494/ galUS

The fluid is acceptable if the concentration is within ±10% of specification.

The engineer may adjust the field J494L rate based on the results of this test.

6.8.3.3 J513 To verify the quality of J513 solutions, follow this procedure.

STEP 01 Prepare standard J513 solutions of 15%, 25%, 35%, and 50%, using 100 mL of location water to dilute the J513.

STEP 02 Measure the conductivity of the standard J513 solutions using the conductivity meter.

STEP 03 Prepare a standard curve of conductivity vs. temperature for various J513 concentrations.

STEP 04 Measure the conductivity of the field-prepared J513 solution.

STEP 05 Determine the volume % of J513 for the field-prepared J513 solution from the standard curve (additional check on SG should be completed to verify the field sample)

STEP 06 Calculate the concentration of J513 in the field sample. It is acceptable if within ±10% of specification.

Note:The volume % J513 determined in Step 06 = galUS J513/galUS of the field sample.

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6.9 Super X emulsion Super X Emulsion (SXE*) is a viscous, highly retarded, concentrated acid system designed for use in matrix acidizing or acid fracturing of carbonate formations. SXE is an oil-external phase emulsion formed with a 70:30 hydrochloric acid-to-oil ratio, stabilized with an emulsifier. Hydrochloric acid (HCl) concentrations ranging from 15% to 28% may be used. SXE is designed for batch-mix operations; however, continuous-mix operations can be performed by following the procedures provided in the field mixing procedures section. The temperature range of SXE is 75 to 375 degF [23 to 191 degC] and emulsion breakout times can be customized by varying the emulsifying agent U108 loading as needed. U108 replaces both U080 (low temperature emulsifier for SXE) and U103 (high temperature emulsifier for SXE-HT).

Caution:Goggles, rubber gloves, and a protective covering must be worn when mixing acids. Always work under a fume hood when preparing acids.

Warning:Always add concentrated acid to water. Do not add water to the acid because the resulting heat could make the acid boil up onto your skin or eyes.


350-mL glass beakers

syringe

15-mL glass tubes

magnetic stirrer

PMC hot-plate stirrer with speed adjustment

Fann 35 with Hestolloy bob/sleeve and fluid cup

kerosene or diesel

HCl, 7.5% to 28%

A166 corrosion inhibitor

U080 emulsifying agent

glass rod

2% KCl.

Follow this procedure to mix the SXE.

STEP 01 Add 140 mL HCl into glass beaker and mix with the magnetic stirrer at a speed high enough to produce a vortex with the stirrer bar. Add the A166 corrosion inhibitor as required and mix until homogeneous.

STEP 02 Place another beaker on the mixing plate and place 60 mL each of kerosene and U080 into the beaker to mix thoroughly with a vortex tip to the bottom of the beaker.

STEP 03 Use a syringe to drop the acid and inhibitor mixture into the oil and U080 mixture while stirring with the tip of the vortex to the beaker bottom.

STEP 04 Increase the mixing speed as high as the mixer can mix, after adding all acid mixture into the oil mixture, for about 15 to 20 min.

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STEP 05 A stable emulsion system should be prepared. Place a small sample of the emulsion into a 15-mL glass tube to observe for 10 min. No separation will be evident if the emulsion is an oil-external stable emulsion.

Another way to check the oil-external property is to tick a drop of emulsion using the glass rod and drop it into a 2% KCl solution in a 15-mL glass tube. If an oil-external emulsion forms, the drop will remain and slowly settle down to the tube bottom; otherwise, the drop will disperse quickly into the solution.

Some commercial diesel is contaminated and not suitable for SXE preparation. If you are having difficulty forming a stable oil-external emulsion, change the source of the oil.

STEP 06 When you obtain a stable oil-external emulsion, check the rheology using the Fann 35 with the Hestolloy bob/sleeve combinations.

6.10 ClearFRAC J508WClearFRAC* fracturing fluids are water-base systems comprising a viscoelastic surfactant (J508W) and a brine. Full fluid viscosity is achieved once the surfactant is completely dispersed in the brine. Viscosity develops rapidly without shear degradation. ClearFRAC fluids can be batch mixed or continuous mixed. Maximum fluid temperature is 240 degF.

To prepare a ClearFRAC solution, you will need the following equipment and materials.


blender jar


timer

pH meter

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thermometer

Fann 35

additives commonly used in ClearFRAC systems (example concentration amount in 500 mL):

M117 potassium chloride 333 lbm/Mgal 20 g

J508W gelling agent 4.0 galUS/Mgal 2.0 mL

J463 (T>150F) HT activator 5 lbm/Mgal 0.3 g.

Follow this procedure to prepare the solution.

STEP 01 Pour 500 mL of water into the blender jar and stir.

STEP 02 Test the fluid temperature.

STEP 03 If the fluid temperature is less than 150 degF, add 20 g of KCl and dissolve it. If the fluid temperature is greater than 150 degF, add 0.3 g of J463 and dissolve it.

STEP 04 Create a vortex to the tip of the stirrer. Slowly add J508 into the mixture. The amount of J508 used will depend on the desired viscosity.

STEP 05 Stir the mixture until the vortex closes.

STEP 06 Place the mixture into the water bath at 70 to 80 degC to get the foam out. The fluid should become clear.

STEP 07 Check the fluid temperature and pH.

STEP 08 Check the fluid viscosity to see if it is in the specified range.

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7.0 MatrixAcidizingFluids

Matrix acidizing fluids are used in acidizing treatments. Table 7-1 shows the acidizing systems most used by Schlumberger.

Table 7-1. Acid Systems Most Used by Schlumberger

Major application Acid systems

Carbonateacidizing HydrichloricacidIntensifiedacid

SandstoneacidizingMudacidClayacidOrganicmudacidOrganicclayacid

GaswellAlcoholicacidGaswellacidGaswellmugacid

Retardedacid DADacidSXE/SXEHT

Gelledacid LCA/SDA/VDA

MudremovalBDAMSRNARS

Organicdamageremoval Cleansweep

Scaledissolving CASU104/U105/U106

PerforatingacidAqueousaceticacidFormicacidPerforatingacid

The following sections describe how to prepare laboratory samples of these acid systems.

7.1 HClThe maximum concentration of commercial HCl is 36%. Table 7-2 lists the hydrochloric acids most used in the oilfield industry. Use this table to prepare 1000 mL of different dilutions of HCl from 36% HCl.

Table 7-2. Dilutions of Concentrated Hydrochloric Aicd

HCI Acid Strength

36% HCI needed

(mL)Density g/cc)

28% 751 1.141

20% 507 1.099

15% 379 1.074

10% 247 1.049

7.5% 183 1.036

5.0% 120 1.024

To prepare 1,000 mL of any concentration of HCl, follow this procedure.

STEP 01 Place approximately 200 mL of water in a 1,000-mL volumetric flask.

STEP 02 Add the required quantity of concentrated HCl (see Table 7-2) into the flask very slowly.

Caution:Heat and odor will be released. It is strongly recommended that this procedure be performed in a fume hood.

52 | Matrix Acidizing Fluids

Caution:Always remember to add acid to water. Never add water to acid.

STEP 03 Finish filling the flask to the graduated line indicating 1,000 mL.

STEP 04 Cap the flask and shake it a few times upside down over a sink or in the fume hood.

7.2 Intensified AcidIntensified acid is a regular inhibited HCl (generally 15%) with 33.8 lbm/1,000 galUS Y001 (0.25%) added.

Note:Y001 is ammonium bifluoride, which combines with water to form HF acid.

It is often used in initial cleanup as well as in dolomitic limestones containing a certain amount of silica. As much as 50% more reaction occurs between intensified acid and dolomitic limestone at surface conditions. The increase is less pronounced at elevated temperatures. Field results also confirm the value of intensified acid as a cleanup treatment in dolomitic limestone formations.

A side reaction product of CaF2 precipitate could cause damage.

To mixing intensified acid, you will need the following equipment and materials:

plastic beaker large enough to hold the acid, inhibitor, and Y001

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magnetic stirrer

HCl base acid

required inhibitor

Y001 (33.8 lbm/1,000 galUS).


STEP 01 Place the required amount of HCl base acid with the required amount of inhibitor into a plastic beaker.

STEP 02 Stir the solution until homogeneous with the magnetic stirrer.

STEP 03 Add the required amount of Y001 (33.8 lbm/1,000 galUS) slowly.

STEP 04 Stir the mixture until the solution becomes clear.

7.3 Clay acidClay acids from Schlumberger are designed specifically for acidizing sensitive sandstone formations. They not only provide good stimulation, but also provide permanent stabilization of clays and other fines, eliminating water sensitivity and the mobility of migratory fines. Clay acids slowly release hydrofluoric acid (HF) from the hydrolysis of fluoboric acid (HBF4) and can penetrate a much greater distance from the wellbore before spending than mud acid can. There are four formulations of clay acid presented here:

full strength clay acid

full strength clay acid LT (low-temperature formulation)

half-strength clay acid

half-strength clay acid LT.

Clay acids are the only acid formulations that require shut-in time. One reason is that they slowly release HF, limiting the amount of HF

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available at any one time. Another reason for shut-in time is the unique feature of borosilicate, a reaction product, to coalesce and form a coating on undissolved particles. This coating of borosilicate will cement the affected clays and fines in place, thus severely limiting further clay migration in the contact area.

Clay acids are generally used from 130 degF to 300 degF, but clay acids LT are only used from 100 degF to 130 degF.

To mix clay acids, you will need the following:

glass beaker

magnetic stirrer

water

Y001

L010

HCl.

To mix a clay acid, refer to Tables 7-1 and 7-2 for additives and quantities. Each formulation prepares 1,000 mL of clay acid.

Note:To prepare clay acid properly, the additives must be added in the order listed in the table (from top to bottom); otherwise, a precipitate will form.

Note:Y006 and L010 have the same composition and can directly replace each other.

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Table 7-3. Formulations for Clay Acids

Ingredients

Full strength clay acid

H813 (SG 1.096)

Half-strength clay acid, H913

(SG 1.047)

Water 680mL 843mL

Y100 120g 60g

35%HCI 194mL 97mL

Y006 60g 30g

Table 7-4. Formulations for Low-Temperature Clay Acids

IngredientsFull strength clay acid LT

H814

Half-strength clay acid, H914

Water 545mL 772mL

Y100 120g 60g

35%HCI 336mL 168mL

Y006 60g 30g

S.G. 1.121 1.047

7.4 Mud acid Mud acid is a mixture of inhibited HCl acid and hydrofluoric acid. Mud acid can not only dissolve the minerals that HCl acid can dissolve, but it can also dissolve siliceous minerals presented in most sandstone formations.

Note:Calcium, magnesium, sodium, and potassium brines can react with HF acid to form insoluble precipitates. Do not use any of these for mixing the solution.


To mix mud acids, you will need the following equipment and materials:

plastic beaker

magnetic stirrer

water

Y001

HCl.

Table 7-5 lists the additives and quantities required to prepare the most common mud acid formulations.

Caution:Because of the safety issues associated with concentrated HF acid, it is strongly recommended to mix the mud acid with the quantities of Y001 inhibitor listed in the table.

To mix mud acid according to Table 7-5, follow this procedure.

Concentration 36% HCI (mL) Y001 (g) Water (mL) Density (g/cc)

4%HCI–0.5%HF6%HCI–0.5%HF8%HCI–0.5%HF

110160210

7.27.27.2

885835785

1.0221.0321.041

6%HCI–1%HF8%HCI–1%HF10%HCI–1%HF

170220270

151515

820770720

1.0361.0451.054

6%HCI–1.5%HF7.5%HCI–1.5%HF10%HCI–1.5%HF12%HCI–1.5%HF

180220290340

24242424

804764694644

1.0411.0481.0611.07

10%HCI–2%HF 300 30 680 1.065

12%HCI–3%HF 380 48 588 1.085

Table 7-5. Mud Acid Formulations

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Caution:Wear safety goggles, protective clothing, and rubber gloves. Work in a fume hood.

STEP 01 Place the appropriate quantity of fresh water in a plastic beaker.

Note:Do not use seawater, oilfield brine, calcium, magnesium, potassium, or sodium chlorides to prepare mud acid.

STEP 02 Add the required amount of Y001. Mix using a magnetic stirrer until the Y001 has dissolved completely.

STEP 03 Add the required quantity of concentrated HCl slowly. Mix until clear.


Caution:Heat will be generated! Be sure always to add acid to the water–never add water to the acid.

7.5 Organic mud acidOrganic mud acid is a mixture of 9% formic acid (HCO2H; also called L36) and 3% HF acid. It is more easily inhibited, has a lower reaction rate, and has less tendency to form asphaltic sludge than HCl acids.

Organic mud acid is recommended for use in high-temperature matrix acidizing and wellbore damage removal in both sandstone and carbonate reservoirs where extended inhibition time is expected and asphaltic sludges are formed when the formation contacts HCl acids.

Warning:Both Y001 and L36 can cause severe eye and skin burns. Wear the proper PPE.

To mix organic mud acids, you will need the following equipment and materials:

1,000-mL plastic beaker

magnetic stirrer

water

A186

Y001

HCl.

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The formula for preparing 1,000 mL is as follows:

fresh water

inhibitor as required

48 g Y001

72 mL 36% HCl

A186

90 mL L36.

Follow this procedure to mix organic mud acid.

STEP 01 Add approximately of fresh water in the plastic beaker. Set magnetic stirrer to a speed high enough to form a vortex.

STEP 02 Add A186 and mix thoroughly.

STEP 03 Add the Y001 into the beaker slowly and stir until totally dissolved.

STEP 04 Add the HCl acid and L36. Stir until the mixture is homogenous.

STEP 05 Fill up the container to the 1,000- mL line with fresh water.

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7.6 Organic clay acidAn organic clay acid (OCA) system is used for acidizing sandstones containing high silt/clay content and for HCl-sensitive formations. It reduces secondary precipitation and fines migration after the treatment. It can remove formation damage caused by clay and other aluminosilicate minerals, and it can be used for high temperature applications.

Tables 7-6 and 7-7 list two OCA formulations (OCA-R and OCA-HT) and the conditions under which they should be applied.

Table 7-6. OCA Formulations

Component OCA-R OCA-HT

HCI 5% 1.5%

J285 5% 5%

L001 13.4% 10%

Y001 5% 2%

Y006 2.5% 1.2%

Table 7-7. Conditions for Using OCA Formulations

Conditions OCA-R OCA-HT

>300F - *

<300F,silt/clay>30% * -

>5%zeolite - *

<5%zeolite * -

>5%chlorite - *

<5%chlorite * -

*Fluidapplicableunderthiscondition-Fluidnotapplicableundertheseconditions

7.7 Alcoholic acidAlcoholic acid is a mixture of acid (HCl or mud acid) and alcohol (F003 or K046). Adding alcohol into the acid

lowers the surface tension

increases the vapor pressure and improves postclean up effectiveness

retards the acid reaction rate and improves success in acidizing low to medium permeability dry gas formations

slightly accelerates the corrosion rate.

The concentration of alcoholic acid mixtures indicates the volume percentage of each additive in the acid. For example, an 80:20 alcoholic acid mixture is prepared by mixing 800 mL of acid (e.g., 15% HCl) and 200 mL of alcohol.

Note:When the mixture mentioned in the text is prepared, there is a volume loss of 10 mL.

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7.8 Dynamic acid dispersion (DAD)A dynamic acid dispersion (DAD) is an acid outside-phase emulsion stabilized with dispersing agent U074. The dispersion simultaneously dissolves the minerals and removes the oily paraffinic deposits.

The dispersion can be prepared with various acids and hydrocarbon solvents. HCl and P121 (toluene) are the most common. Ratios of acid:hydrocarbon can be made from 10 to 50%. Usually 15 galUS of U074 per 1,000 galUS of acid is used to stabilize the emulsion.

To mix a DAD, you will need the following equipment and materials:

Waring blender

1,000-mL glass beaker

HCl acid

appropriate corrosion inhibitor

P121.

Use this procedure to mix a DAD.

Caution:The fumes are hazardous. Prepare the DAD under a fume hood or use appropriate precautions. Wear all appropriate PPE.

STEP 01 Prepare 450 mL of 15% HCl acid. Add appropriate corrosion inhibitor for suitable protection time.

STEP 02 Place 50 mL of P121 in a Waring blender cup. Add the required quantity of U074. Set the speed on the blender to create a vortex down to the blades of the blender. Mix for 3 min.

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STEP 03 Continue mixing while slowly adding acid through the hole in the blender cup lid. Add a volume equal to the volume of the P121 and the U074 mixture prepared in Step 02.

STEP 04 Increase the speed of the Waring blender to around 1,000 rpm. Mix for 10 min. An oil-outside phase dispersion should form. The fluid will have some viscosity and may stick to the sides of the blender cup. This is the seed batch dispersion.

STEP 05 Continue mixing slowly, and steadily add the acid solution through the hole in the blender lid to the seed batch. The emulsion should invert to become acid-outside phase. The fluid should wet the sides of the blender cup and easily drain down the sides of the cup.

STEP 06 Mix 15 min more at 1,000 rpm.

Note:The DAD cannot be stored for long durations.


8.0 QA/QCPractices

All fluids used in fracturing treatments must be tested to ensure quality and conformance with the design requirements. The following sections describe QA/QC procedures for these tests.

8.1 Fracture fluid QA/QCThe following tests are required:

Perform API water analysis on all location water samples. Analysis will include pH and chloride, carbonate, bicarbonate, and iron concentrations.

Perform silicate analysis for all PrimeFRAC, YF800HT, and YF800LpH fluids. Silicates should be less than 25 ppm.

Perform bacteria analysis upon request. Bacteria should be less than 3,000,000 per L.

Test all concentrated KCl tanks for total hardness. Total hardness should be less than 400 ppm.

Test all unfamiliar water sources (e.g., pond or lake water) and low polymer systems (e.g., PrimeFRAC) for total hardness. Total hardness should be less than 400 ppm.

Total hardness strips can be used to analyze the hardness of water. If the total hardness strips indicate values of 425 or greater, use the Hach kit for more accurate determination. The strips are not reliable for high concentrations.

Perform sand sieve analysis on all proppant samples. Of the proppant, 90% must fall within the screen size specified for that proppant for a particular job. Typically,

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you should have one proppant sample for every 50,000 lbm of proppant.

Check field additives for pH, appearance, and odor. pH paper may be used for additives, but if a problem is observed, double check the additive with the pH meter.

Prepare a base gel for each fracture tank and check (i.e., if there are six tanks, then six linear gel tests must be performed). The base gel viscosity must fall within the acceptable range before ANY rheological characteristics are measured. Fluid pH will also be checked with a pH probe to ensure the proper pH range (6.0 to 8.0) for polymer hydration.

Verify crosslinked gel properties (pH measured using a pH probe, initial crosslink temperature, and gel lip test) for each fracture tank before measuring rheological properties. The initial crosslink temperature should be within 2 degF of the requested value.

Evaluate the crosslinked gel viscosity using composite water samples and a Fann 50-type rheometer at 100 sec-1.

Note:If there are fewer water samples than requested Fann tests, then do not use composite samples.

Composite samples are to be prepared using no more than three water samples for a single composite sample (i.e., composite 1 can be made up of samples from tanks 1, 2, and 3; while composite 2 can be made

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60 | QA/QC Practices

up of samples from tanks 4, 5, and 6, but no composite can be made up of samples from 4 or more water samples). Use different composite samples for different Fann runs to be sure that all water samples are tested. Use 52-mL samples and API RP39 procedures unless otherwise specified.

Note:45-mL samples can be used when bob-climb problems are observed. Perform tests for 20 min longer than the job pump time.

Perform break tests with live active breakers using a Fann 50-type rheometer. When using encapsulated breakers, 800- psi overburden pressure is preferred to minimize nonrepresentative release of breaker (400 psi is the minimum pressure regardless of breaker type). To minimize testing, crosslinked gel can be tested with the appropriate amount of encapsulated breaker and be considered similar to those in the absence of breaker, provided the coating is stable at test temperature.

The current rule of thumb for determining the lifetime of a fracturing fluid is the time at which the viscosity falls below 100 cp at a shear rate of 100 sec-1 (300 cp at a shear rate of 40 sec-1, or 80 cp at a shear rate of 170 sec-1), or below a requested level.

Location water should be used for determining break times. Source water can be used if location water is not available with sufficient time for laboratory testing. In such case, a test should be performed with location water to verify test results.

Problems with laboratory testing should be communicated with senior laboratory personnel and the fracturing department.

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Changes in the fluid design or problems with the testing must be communicated to the laboratory manager and the fracturing department.

If the laboratory cannot correct poor test results, the fracturing department must be notified directly. The laboratory report should include results, description of problem, and likely source/solution of problem.

High rheology data (e.g., in excess of 1,500 cp for nonramp or nonspike data) may indicate overdesign of fracturing fluid and the fracturing department should be notified.

The fracturing fluid design test results will be plotted on a standard format. The report will be sent to the field or sales engineer requesting the tests.

8.2 Fracture fluid additives QA/QCField additives must be checked for pH, appearance, and odor. pH paper may be used for additives, but if a problem is observed, double check with the pH meter. The pH should fall within the range listed in Table 8- 1 for common fracturing additives. If additive problems are suspected, then measure conductivity and specific gravity. Measure conductivity for all crosslinkers and titrate all buffers and activators to determine actual concentration.

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Additive Description pH Range Color Specific gravity Conductivity [mS at 70 degF]

F103 Surfactant 5to7 Colorless 0.94 53to63

F103/W54 50:50mixture 5to7 Clear–yellow 0.94 0.7to1.7

F104 Foamingagent 7to9 Clear–amber 1.02

F802 Surfactantblend

6to7 Amber 0.92

J353L Hightemperaturegel

stabilizer

7to9 Lightyellow 1.3 128to135

J450 Stabilizer 11.5 Colorless 1.12

J464L Buffer(0.5lbm/galUS)

8to9.5 Colorless 1.03 34to36

J488 Acidbuffer 5.5to6 Colorless 1.09to1.13 62to65

J494L Buffer(1.0lbm/galUS)

9to11 Colorless 1.06to1.08

J508W Viscoelasticsufractant

6to9 Yellow–brown 0.93

J511 Delayagentsolution

6to7 Clear 1.07to1.12

J513(25%) Zirconatecrosslinker

6to7 Yellow–brown 1.05 38to40

J515(25%) Zirconatecrosslinker

6to7 Yellow–brown 1.05 15to17

J877 HPGdieselslurry

6to7(paper) Amber 1.06to1.09 –

J916 CMHPGdieselslurry

6to7(paper) Amber 1.06to1.09 –

L010Solution 3wt%boratecrosslinker

4to6 Colorless 1.02 0.3to0.6

L064 KCIsubstitute 5to7 Colorless 1.01 62to85

L401 Acidbuffer(aceticacid)

<4 Colorless 1.02

LGDX/LSolution

Boratecrosslinker(0.7ppgL10,0.5gpg

U28)

>13 Colorless 1.22 220

U028(10%) Caustic >10 Colorless 1.04

W054 Nonemulsifyinggagent

6to7 Clear–yellow 0.88

Table 8-1. Physical Properties of Various Fracturing Fluid Additives


8.2.1 J515 To prepare the J515 test solution, you will need the following equipment and materials.

100-mL volumetric flask


local water

J515 sample.


STEP 01 Prepare standard J515 solutions (e.g., 15, 25, and 35%) using the 100-mL volumetric flask and the local water to dilute the J515.

STEP 02 Measure the conductivity of the solutions using the Orion Model 130A conductivity meter. Prepare a standard curve of conductivity reading versus temperature for various volume% J515.

STEP 03 Measure the conductivity of the field-prepared J515 solution.

STEP 04 Determine the volume % J515 for the field-prepared solution from the standard curve. An additional check of the specific gravity should be completed to verify the field sample. Table 8-2 shows the SG for specific dilutions and conductivities.

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Table 8-2. Specific Gravity of J515 Dilutions and Conductivities

J515 Dilution [volume %]

Conductivity at 70 degF Specific gravity

5 5.7 1.01

12.5 10.2 1.03

20 13.7 1.04

25 15.6 1.05

35 18.2 1.07

50 19.6 1.08

100(raw) ~14 1.22

STEP 05 Calculate the concentration of J515 in the field sample. The J515 fluid is acceptable if its concentration is within ±10% of specification. To find the concentration to use in the field sample, use this equation:

(volume % J515 determined in Step 5)/100 = galUS J515/galUS of the field sample

8.2.2 LGD Crosslinker To test LGD crosslinker, you will need the following equipment and materials:

beaker


local water

LGD crosslinker.


STEP 01 Prepare a standard LGD crosslinker solution of 0.7 ppg L010, 0.5 gpg U028, and 0.45 gpg water, using the local water.

STEP 02 Measure the conductivity of the test solution using an Orion Model 130A conductivity meter. Prepare a standard curve of conductivity reading versus temperature.

STEP 03 Measure the conductivity on the field-prepared LGD crosslinker solution.

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STEP 04 Compare the conductivity of the field-prepared LGD crosslinker solution with the standard curve.

For this test solution, if the conductivity at 70 degF is 220 mS, the specific gravity should be 1.22. Complete an additional check of the specific gravity to verify the field sample.

8.2.3 U028To test the quality of a U028 fluid, you will need the following equipment and materials:

beaker

DI or distilled water

U028 sample

0.1N HCl acid

phenolphthalein indicator.


STEP 01 Dilute 1 mL of U028 sample to approximately 50 mL using distilled or deionized water.

STEP 02 Add 3 drops (0.25 mL) of phenolphthalein indicator (pink to colorless endpoint).

STEP 03 Titrate with 0.100 N HCl to the clear/colorless endpoint.

STEP 04 Calculate concentration of U028:

0.100 N HCl (mL) = % U028

The fluid is acceptable if the concentration of U028 is within ±10% of specification. The field engineer can adjust the field U028 add rate based on the concentration.

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9.0 References

These sources will provide more information on stimulation laboratory procedures:

Well Services Safety Standard 24: Laboratory Operation, InTouch Content ID# 3313702

Key Service Quality Requirements for Stimulation, InTouch Content ID# 4147783

Fracturing Engineering Manual Section 900, Acid Fracturing, InTouch Content ID# 3015576

Fracturing Engineering Manual Section 1200 Appendix B –Fracturing Fluids, InTouch Content ID# 3015580

Fracturing Engineering Manual Section 1300 Appendix C –Additives, InTouch Content ID# 3012434

Fracturing Materials Manual volume I and II: Fluids InTouch Content ID# 4223817

Matrix Materials Manual, InTouch Content ID# 4013354

Stimulation client support lab procedures and information, InTouch Content ID# 3948499.

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66 | References


10.0 CheckYourUnderstanding


1. Choose all true statements regarding eye protection in the laboratory.A. Safety glasses with fixed side shields

are required at all times as minimum eye protection (does not apply to offices, rest rooms, or other protected areas not in the laboratory working area).

B. Indirect vented chemical goggles must be worn when handling chemicals such as cement, unless these chemicals are in sealed containers.

C. Face shields must be worn when handling hot liquids, acids, or liquids that are under pressure, working with flammable liquids where the flash point is less than 100 degF.

D. Visitors must wear safety glasses with side shields while in the laboratory work areas.

E. All of the above are true.

2. Select two correct statements regarding protective clothing in the laboratoryA. Laboratory coats with long sleeves

must be worn.B. Rubber or plastic protective aprons

must be worn, depending on the type of chemical. Read the MSDSs for the protective clothing requirements.

C. Types of clothing that allows exposure to a large area of skin can be worn in a laboratory, e.g., sleeveless tops, short skirts, or short pants.

D. Safety boots are not required in the laboratory. Shoes that provide protection from liquids must be worn, such as a leather shoe that covers the foot. Sandals and open shoes are not permitted.

3. Which of the following quality assurance tasks should be done on location before pumping?A. Check the amount of water in each

tank, take water sample from each tank, and test the samples.

B. Test linear gel viscosity from the outlet of the PCM/GelSTREAK.

C. Check all the amounts of additives; recalculate to make sure enough for the job is available.

D. Test the crosslinker and all additives. E. All of the above are true.

68 | Check Your Understanding

4. Which of the following quality assurance tasks should be performed during pumping?A. Throughout the job, the linear gel

should be continually checked for viscosity and temperature to confirm the proper gel loading of the gel.

B. Samples should be taken from the outlet of the blender or fracture pumps to test the delay time of the cross-linked fluid as well as pH, temperature, bottomhole temperature stability, and break testing (water bath).

C. The physical quantities of all liquid and dry additives should be continually checked throughout the job to compare to the designed amount to be pumped.

D. All of the above should be done.

5. Choose the correct statement regarding API gravity. A. The equation relating specific gravity to

API gravity isSG= 141.5

131.5 + API

B. The higher the API gravity is, the heavier the fluid is.

C. The higher the API gravity is, the lighter the fluid is.

D. Both A and C are true. E. None of the above is true.

6. Which statement regarding pH is incorrect?A. The normal pH range for brines is

between 6 to 8. B. The normal pH range for fracture fluids

is 11 to 12.C. A low pH may indicate spent acid.D. A high pH may indicate contamination

by mud or filtrate.

7. Which statements are true regarding specific gravity?A. Specific gravity is the ratio of the

weight of material to the weight of water, or the density of the material to the density of water.

B. The higher the specific gravity is, the heavier the liquid is.

C. Specific gravity can be used to differentiate hydrocarbons (condensate) from water. Fresh water has a specific gravity of 1.000.

D. A hydrometer is the device used to measure specific gravity.


8. Alkalinity tests include _________ .A. SG and pH testsB. bicarbonates, carbonates, and

hydroxide testC. all of the aboveD. none of the above

9. Choose all correct statements about bicarbonates. A. Bicarbonates are very important for

fracture fluid quality control.B. Fracturing fluids require various

bicarbonate concentrations, depending on the specific fluid.

C. High bicarbonates will tend to slow gel hydration and delay fluid crosslinking.

D. High bicarbonate levels may be characterized by a high pH or be an indication of carbonates present in the water.



10. Choose the correct statement(s) regarding carbonates and hydroxides:A. Most formations contain high levels of

carbonates or hydroxides. B. If the water sample contains carbonate

and/or hydroxide, it may be a clue to a problem in the customer’s well, possibly indicating the presence of some drilling mud contamination.

C. Most oilfield waters will contain only bicarbonates, but occasionally carbonate and/or hydroxide will be present.

D. None of the above are true.

11. Choose the correct statement about chloride. A. Most fracture fluids today comprise 2%

KCl.B. The chloride content of a 2% KCl

solution should be approximately 9,600 mg/L.

C. The chloride test can also be used to determine if a sample is spent acid.

D. All of the above are true.

12. How would you identify H2S in the sample? A. The water sample is very cloudy. B. The sample smells like rotten eggs. C. The sample has large particles floating

in it. D. None of the above are true.

13. The hardness tests include a test for _________. A. sulfur and magnesiumB. calcium and magnesiumC. calcium and potassiumD. sodium and potassium

14. Choose all true statements regarding iron:A. When high iron is encountered in

fracture mix water, breaker J218 (ammonium persulfate) will have an accelerated effect.

B. In high iron environments, J218 may cause premature break of the fracturing fluid.

C. High iron content will interfere with the crosslinking of the fracturing fluid, resulting in poor crosslink integrity.

D. The maximum iron concentration for fracture water ranges from 8 ppm to 25 ppm, depending on the fluid.


15. Which instrument is used to determine viscosity of linear fluids? A. spectrophotometerB. Fann® Model 35 rheometer (Fann35) C. hydrometerD. none of the above

16. What is the vortex closure test?A. The vortex closure test indicates the

onset of viscosity development, and rarely coincides with full crosslinking.

B. The vortex closure test indicates full crosslinking.

C. None of the above are true.


17. What are three distinct fluid behaviors during a vortex closure test in the order in which they occur? 1. fluid crowning, which is the formation

of a dome of fluid over the center of the blender cup (over the blades). This is the point at which the fluid no longer completely circulates in the blender cup

2. viscosity increase that results in closure of the vortex, but does not stop fluid circulation in the blender cup

3. linear fluid behavior, characterized by a deep vortex

___ A. 1, 2, 3___ B. 2, 3, 1___ C. 3, 2, 1___ D. 1, 3, 2

18. Which statement is true regarding the static gel break test? A. The static gel break test tests for the

time at which the gel breaks enough to flow back.

B. A gel is usually considered broken enough to flow back when it has degraded to a viscosity of 20 cp at the required temperature.

C. This test is important for the field operation that does not have high-pressure, high-temperature (HPHT) gel break test equipment.


19. What instrument is used to perform a crosslinked gel breaking test when a BHT is above 100 degC? A. a Fann Model 35 type rheometerB. a Fann Model 50 type rheometer C. a Waring blender

D. none of the above

20. What is the proppant turbidity test used for?A. to determine the shape of the sand B. to determine the cleanliness of the

fracture sand (amount of fines)C. to determine the toughness of the sandD. none of the above

21. Which statement is true about the fracturing fluids? A. The Widefrac 100HTD (YF*100HTD)

fracturing fluids are water-base systems comprising a refined guar gelling agent crosslinked by a borate-type crosslinker.

B. YF800HT fluids are temperature-activated, zirconate-crosslinked water-base fluids that use CMHPG as a gelling agent.

C. YFGOIII is a gelled, oil-base fluid used as a fracturing fluid for the treatment of water-sensitive formations. Diesel, kerosene, condensate, and a wide variety of crude oils can be used to prepare YFGOIII.


22. Which is true about SXE (Super X Emulsion)? A. SXE is a viscous, highly retarded,

concentrated acid system designed for use in matrix acidizing or acid fracturing of carbonate formations.

B. SXE is an oil-external phase emulsion formed with a 70:30 HCl-to-oil ratio, stabilized with an emulsifier.

C. HCl concentrations ranging from 15% to 28% may be used.

D. The temperature range of SXE is 75 to 375 degF [23 to 191 degC].



23. Which of the following systems are most used for carbonate acidizing? A. DAD, SXEB. HClC. mud acid, clay acidD. none of the above

24. Which of the following systems are most used for sandstone acidizing?A. DAD, SXEB. HClC. mud acid, clay acidD. none of the above

25. What is mud acid? A. a mixture of clay acid and acetic acidB. a mixture of inhibited HCl acid and

hydrofluoric acid. C. a mixture that can not only dissolve the

minerals that HCl acid can dissolve, but can also dissolve siliceous minerals presented in most sandstone formations.

D. b and c E. none of the above

26. What does DAD stand for?A. diluted acid dispersionB. dynamic acid dispersionC. diffusion additives dispersionD. none of the above

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